<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>V-I vs I-V Graph Gradients</title>
  <script src="{{VENDOR_CDN}}/gsap.min.js"></script>
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: transparent;
      color: #0f172a;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
      user-select: none;
    }

    /* Controls */
    .controls {
      display: flex;
      gap: 8px;
      margin-bottom: 12px;
      background: #f1f5f9;
      padding: 4px;
      border-radius: 9999px;
      border: 1px solid #e2e8f0;
    }

    .pill-btn {
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 600;
      border-radius: 9999px;
      border: none;
      background: transparent;
      color: #64748b;
      cursor: pointer;
      transition: all 0.25s ease;
    }

    .pill-btn.active {
      background: #ffffff;
      color: #0f172a;
      box-shadow: 0 1px 4px rgba(0, 0, 0, 0.1);
    }

    /* Grid Layout */
    .comparison-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 16px;
      width: 100%;
      max-width: 640px;
    }

    @media (max-width: 420px) {
      .comparison-grid {
        grid-template-columns: 1fr;
        gap: 12px;
      }
    }

    .graph-panel {
      display: flex;
      flex-direction: column;
      align-items: center;
      background: rgba(255, 255, 255, 0.6);
      border-radius: 12px;
      padding: 8px 4px;
    }

    /* Badges */
    .badge {
      font-size: 13px;
      font-weight: 700;
      padding: 3px 10px;
      border-radius: 6px;
      margin-bottom: 6px;
    }

    .badge-vi {
      background: #dbeafe;
      color: #1d4ed8;
    }

    .badge-iv {
      background: #ede9fe;
      color: #6d28d9;
    }

    /* SVG Graph styling */
    .graph-svg {
      width: 100%;
      max-width: 220px;
      height: auto;
      overflow: visible;
    }

    .axis-line {
      stroke: #64748b;
      stroke-width: 1.75;
      stroke-linecap: round;
    }

    .axis-arrow {
      fill: #64748b;
    }

    .axis-text {
      font-size: 13px;
      font-weight: 700;
      fill: #334155;
      font-family: inherit;
    }

    .line-vi {
      stroke: #2563eb;
      stroke-width: 3;
      stroke-linecap: round;
    }

    .line-iv {
      stroke: #7c3aed;
      stroke-width: 3;
      stroke-linecap: round;
    }

    .triangle-fill-vi {
      fill: rgba(37, 99, 235, 0.08);
      stroke: #2563eb;
      stroke-width: 1.5;
      stroke-dasharray: 4 3;
    }

    .triangle-fill-iv {
      fill: rgba(124, 58, 237, 0.08);
      stroke: #7c3aed;
      stroke-width: 1.5;
      stroke-dasharray: 4 3;
    }

    .delta-text {
      font-size: 11px;
      font-weight: 700;
      font-family: inherit;
    }

    .delta-vi-v { fill: #2563eb; }
    .delta-vi-i { fill: #2563eb; }
    .delta-iv-i { fill: #7c3aed; }
    .delta-iv-v { fill: #7c3aed; }

    /* Formula & Summary */
    .formula-box {
      margin-top: 6px;
      text-align: center;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 4px;
    }

    .math-row {
      display: inline-flex;
      align-items: center;
      font-size: 14px;
      font-weight: 700;
      color: #1e293b;
      gap: 4px;
    }

    .fraction {
      display: inline-flex;
      flex-direction: column;
      align-items: center;
      vertical-align: middle;
      font-size: 13px;
      line-height: 1.1;
      padding: 0 2px;
    }

    .numerator {
      border-bottom: 1.5px solid #475569;
      width: 100%;
      text-align: center;
      padding-bottom: 1px;
    }

    .denominator {
      width: 100%;
      text-align: center;
      padding-top: 1px;
    }

    .c-vi { color: #2563eb; }
    .c-iv { color: #7c3aed; }

    .tag-rule {
      font-size: 12px;
      font-weight: 600;
      padding: 2px 8px;
      border-radius: 4px;
      margin-top: 2px;
    }

    .tag-rule-vi {
      background: #eff6ff;
      color: #1d4ed8;
      border: 1px solid #bfdbfe;
    }

    .tag-rule-iv {
      background: #f5f3ff;
      color: #6d28d9;
      border: 1px solid #ddd6fe;
    }
  </style>
</head>
<body>

  
  <div class="controls">
    <button id="btnLow" class="pill-btn active" onclick="setResistance('low')">Low R (2 Ω)</button>
    <button id="btnHigh" class="pill-btn" onclick="setResistance('high')">High R (10 Ω)</button>
  </div>

  <div class="comparison-grid">
    
    
    <div class="graph-panel">
      <span class="badge badge-vi">V–I Graph</span>
      
      <svg class="graph-svg" viewBox="0 0 170 145">
        
        <defs>
          <marker id="arrow" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="5" markerHeight="5" orient="auto-start-reverse">
            <path d="M 0 1 L 8 5 L 0 9 z" class="axis-arrow"/>
          </marker>
        </defs>

        
        <line x1="30" y1="125" x2="30" y2="12" class="axis-line" marker-end="url(#arrow)" />
        <text x="14" y="20" class="axis-text">V</text>

        
        <line x1="30" y1="125" x2="160" y2="125" class="axis-line" marker-end="url(#arrow)" />
        <text x="156" y="140" class="axis-text">I</text>

        <text x="20" y="136" font-size="10" fill="#94a3b8" font-weight="600">0</text>

        
        <polygon id="triVI" points="30,125 130,125 130,85" class="triangle-fill-vi" />
        
        
        <text id="lblVI_dI" x="80" y="137" text-anchor="middle" class="delta-text delta-vi-i">ΔI</text>
        <text id="lblVI_dV" x="135" y="108" class="delta-text delta-vi-v">ΔV</text>

        
        <line id="lineVI" x1="30" y1="125" x2="148" y2="78" class="line-vi" />
      </svg>

      <div class="formula-box">
        <div class="math-row">
          <span>Gradient =</span>
          <div class="fraction">
            <span class="numerator c-vi">ΔV</span>
            <span class="denominator c-vi">ΔI</span>
          </div>
          <span>= <strong class="c-vi">R</strong></span>
        </div>
        <div id="statusVI" class="tag-rule tag-rule-vi">Shallow line = Low R</div>
      </div>
    </div>

    
    <div class="graph-panel">
      <span class="badge badge-iv">I–V Graph</span>
      
      <svg class="graph-svg" viewBox="0 0 170 145">
        
        <line x1="30" y1="125" x2="30" y2="12" class="axis-line" marker-end="url(#arrow)" />
        <text x="16" y="20" class="axis-text">I</text>

        
        <line x1="30" y1="125" x2="160" y2="125" class="axis-line" marker-end="url(#arrow)" />
        <text x="156" y="140" class="axis-text">V</text>

        <text x="20" y="136" font-size="10" fill="#94a3b8" font-weight="600">0</text>

        
        <polygon id="triIV" points="30,125 100,125 100,30" class="triangle-fill-iv" />
        
        
        <text id="lblIV_dV" x="65" y="137" text-anchor="middle" class="delta-text delta-iv-v">ΔV</text>
        <text id="lblIV_dI" x="105" y="80" class="delta-text delta-iv-i">ΔI</text>

        
        <line id="lineIV" x1="30" y1="125" x2="112" y2="16" class="line-iv" />
      </svg>

      <div class="formula-box">
        <div class="math-row">
          <span>Gradient =</span>
          <div class="fraction">
            <span class="numerator c-iv">ΔI</span>
            <span class="denominator c-iv">ΔV</span>
          </div>
          <span>=</span>
          <div class="fraction">
            <span class="numerator">1</span>
            <span class="denominator c-iv">R</span>
          </div>
        </div>
        <div id="statusIV" class="tag-rule tag-rule-iv">Steep line = Low R</div>
      </div>
    </div>

  </div>

  <script>
    const data = {
      low: {
        vi: { lineX2: 148, lineY2: 80, triX: 130, triY: 86, dIX: 80, dVY: 108 },
        iv: { lineX2: 110, lineY2: 18, triX: 98,  triY: 30, dVX: 64, dIY: 80 },
        textVI: "Shallow line = Low R",
        textIV: "Steep line = Low R"
      },
      high: {
        vi: { lineX2: 110, lineY2: 18, triX: 98,  triY: 30, dIX: 64, dVY: 80 },
        iv: { lineX2: 148, lineY2: 80, triX: 130, triY: 86, dVX: 80, dIY: 108 },
        textVI: "Steep line = High R",
        textIV: "Shallow line = High R"
      }
    };

    let currentState = 'low';

    function setResistance(state) {
      if (currentState === state && window._initDone) return;
      currentState = state;
      window._initDone = true;

      document.getElementById('btnLow').classList.toggle('active', state === 'low');
      document.getElementById('btnHigh').classList.toggle('active', state === 'high');

      const target = data[state];

      document.getElementById('statusVI').textContent = target.textVI;
      document.getElementById('statusIV').textContent = target.textIV;

      if (window.gsap) {
        // V-I Animation
        gsap.to('#lineVI', { duration: 0.45, attr: { x2: target.vi.lineX2, y2: target.vi.lineY2 }, ease: "power2.out" });
        gsap.to('#triVI', { duration: 0.45, attr: { points: `30,125 ${target.vi.triX},125 ${target.vi.triX},${target.vi.triY}` }, ease: "power2.out" });
        gsap.to('#lblVI_dI', { duration: 0.45, attr: { x: target.vi.dIX }, ease: "power2.out" });
        gsap.to('#lblVI_dV', { duration: 0.45, attr: { x: target.vi.triX + 5, y: target.vi.dVY }, ease: "power2.out" });

        // I-V Animation
        gsap.to('#lineIV', { duration: 0.45, attr: { x2: target.iv.lineX2, y2: target.iv.lineY2 }, ease: "power2.out" });
        gsap.to('#triIV', { duration: 0.45, attr: { points: `30,125 ${target.iv.triX},125 ${target.iv.triX},${target.iv.triY}` }, ease: "power2.out" });
        gsap.to('#lblIV_dV', { duration: 0.45, attr: { x: target.iv.dVX }, ease: "power2.out" });
        gsap.to('#lblIV_dI', { duration: 0.45, attr: { x: target.iv.triX + 5, y: target.iv.dIY }, ease: "power2.out" });
      } else {
        // Direct fallback
        document.getElementById('lineVI').setAttribute('x2', target.vi.lineX2);
        document.getElementById('lineVI').setAttribute('y2', target.vi.lineY2);
        document.getElementById('triVI').setAttribute('points', `30,125 ${target.vi.triX},125 ${target.vi.triX},${target.vi.triY}`);
        document.getElementById('lblVI_dI').setAttribute('x', target.vi.dIX);
        document.getElementById('lblVI_dV').setAttribute('x', target.vi.triX + 5);
        document.getElementById('lblVI_dV').setAttribute('y', target.vi.dVY);

        document.getElementById('lineIV').setAttribute('x2', target.iv.lineX2);
        document.getElementById('lineIV').setAttribute('y2', target.iv.lineY2);
        document.getElementById('triIV').setAttribute('points', `30,125 ${target.iv.triX},125 ${target.iv.triX},${target.iv.triY}`);
        document.getElementById('lblIV_dV').setAttribute('x', target.iv.dVX);
        document.getElementById('lblIV_dI').setAttribute('x', target.iv.triX + 5);
        document.getElementById('lblIV_dI').setAttribute('y', target.iv.dIY);
      }
    }

    setResistance('low');
  </script>
</body>
</html>

Determining Resistance from Linear Graph Gradients

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    }
    body {
      background: #ffffff;
      color: #1e2945;
      padding: 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 100%;
    }
    .graph-container {
      width: 100%;
      max-width: 520px;
      position: relative;
    }
    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }
    .axis-line {
      stroke: #64748b;
      stroke-width: 2;
      stroke-linecap: round;
    }
    .grid-line {
      stroke: #f1f5f9;
      stroke-width: 1.5;
    }
    .axis-label {
      font-size: 13px;
      font-weight: 700;
      fill: #475569;
    }
    .tick-label {
      font-size: 11px;
      fill: #94a3b8;
      font-weight: 500;
    }
    .line-a {
      stroke: #16a34a;
      stroke-width: 3.5;
      stroke-linecap: round;
    }
    .line-b {
      stroke: #d97706;
      stroke-width: 3.5;
      stroke-linecap: round;
    }
    .ref-line {
      stroke: #94a3b8;
      stroke-width: 1.5;
      stroke-dasharray: 4 4;
    }
    .badge {
      font-size: 11px;
      font-weight: 700;
      padding: 4px 8px;
      border-radius: 6px;
      display: inline-flex;
      align-items: center;
      gap: 4px;
    }
    .badge-a {
      background: #dcfce7;
      color: #15803d;
      border: 1px solid #bbf7d0;
    }
    .badge-b {
      background: #fef3c7;
      color: #b45309;
      border: 1px solid #fde68a;
    }
    .controls {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 12px;
      margin: 8px 0;
      width: 100%;
      max-width: 480px;
    }
    .slider-label {
      font-size: 12px;
      font-weight: 600;
      color: #475569;
      white-space: nowrap;
    }
    input[type="range"] {
      flex: 1;
      accent-color: #2563eb;
      cursor: pointer;
      height: 6px;
    }
    .summary-card {
      width: 100%;
      max-width: 520px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 8px 12px;
      display: flex;
      justify-content: space-around;
      align-items: center;
      font-size: 12px;
      font-weight: 600;
      text-align: center;
      gap: 8px;
    }
    .rule-pill {
      display: flex;
      flex-direction: column;
      gap: 2px;
    }
    .rule-pill span.title {
      font-size: 10px;
      text-transform: uppercase;
      letter-spacing: 0.5px;
      color: #64748b;
    }
    .rule-pill span.val {
      color: #0f172a;
    }
    .divider {
      width: 1px;
      height: 24px;
      background: #cbd5e1;
    }
  </style>
</head>
<body>

  <div class="graph-container">
    <svg viewBox="0 0 420 250">
      
      <line x1="60" y1="30" x2="390" y2="30" class="grid-line" />
      <line x1="60" y1="75" x2="390" y2="75" class="grid-line" />
      <line x1="60" y1="120" x2="390" y2="120" class="grid-line" />
      <line x1="60" y1="165" x2="390" y2="165" class="grid-line" />
      <line x1="142.5" y1="30" x2="142.5" y2="210" class="grid-line" />
      <line x1="225" y1="30" x2="225" y2="210" class="grid-line" />
      <line x1="307.5" y1="30" x2="307.5" y2="210" class="grid-line" />

      
      
      <line x1="60" y1="210" x2="60" y2="20" class="axis-line" />
      <polyline points="56,26 60,18 64,26" fill="none" stroke="#64748b" stroke-width="2" stroke-linejoin="round" />
      <text x="35" y="24" class="axis-label" text-anchor="middle">I (A)</text>

      
      <line x1="60" y1="210" x2="395" y2="210" class="axis-line" />
      <polyline points="389,206 397,210 389,214" fill="none" stroke="#64748b" stroke-width="2" stroke-linejoin="round" />
      <text x="390" y="235" class="axis-label" text-anchor="middle">V (V)</text>

      
      <text x="52" y="214" class="tick-label" text-anchor="end">0</text>
      <text x="52" y="169" class="tick-label" text-anchor="end">1.0</text>
      <text x="52" y="124" class="tick-label" text-anchor="end">2.0</text>
      <text x="52" y="79" class="tick-label" text-anchor="end">3.0</text>
      <text x="52" y="34" class="tick-label" text-anchor="end">4.0</text>

      <text x="142.5" y="225" class="tick-label" text-anchor="middle">5</text>
      <text x="225" y="225" class="tick-label" text-anchor="middle">10</text>
      <text x="307.5" y="225" class="tick-label" text-anchor="middle">15</text>
      <text x="390" y="225" class="tick-label" text-anchor="middle">20</text>

      
      
      <line x1="60" y1="210" x2="390" y2="30" class="line-a" />
      
      <line x1="60" y1="210" x2="390" y2="165" class="line-b" />

      
      <line id="vRefLine" x1="225" y1="210" x2="225" y2="30" class="ref-line" />
      <line id="iARefLine" x1="60" y1="120" x2="225" y2="120" class="ref-line" stroke="#16a34a" />
      <line id="iBRefLine" x1="60" y1="187.5" x2="225" y2="187.5" class="ref-line" stroke="#d97706" />

      
      <circle id="dotA" cx="225" cy="120" r="5" fill="#16a34a" />
      <circle id="dotB" cx="225" cy="187.5" r="5" fill="#d97706" />

      
      <g transform="translate(245, 50)">
        <rect x="0" y="0" width="155" height="36" rx="6" fill="#f0fdf4" stroke="#86efac" stroke-width="1" />
        <text x="8" y="15" font-size="11" font-weight="700" fill="#15803d">Resistor A (5 Ω)</text>
        <text x="8" y="28" font-size="9.5" font-weight="600" fill="#16a34a">Steep = Low Resistance</text>
      </g>

      <g transform="translate(245, 125)">
        <rect x="0" y="0" width="155" height="36" rx="6" fill="#fffbeb" stroke="#fcd34d" stroke-width="1" />
        <text x="8" y="15" font-size="11" font-weight="700" fill="#b45309">Resistor B (20 Ω)</text>
        <text x="8" y="28" font-size="9.5" font-weight="600" fill="#d97706">Shallow = High Resistance</text>
      </g>
    </svg>
  </div>

  
  <div class="controls">
    <span class="slider-label">Test Voltage: <strong id="vDisplay">10 V</strong></span>
    <input type="range" id="vSlider" min="2" max="20" value="10" step="1" aria-label="Voltage Slider">
  </div>

  
  <div class="summary-card">
    <div class="rule-pill">
      <span class="title">I-V Graph (Current vs Voltage)</span>
      <span class="val">Steeper = <strong>Lower R</strong></span>
    </div>
    <div class="divider"></div>
    <div class="rule-pill">
      <span class="title">V-I Graph (Voltage vs Current)</span>
      <span class="val">Steeper = <strong>Higher R</strong></span>
    </div>
  </div>

  <script>
    const slider = document.getElementById('vSlider');
    const vDisplay = document.getElementById('vDisplay');
    const vRefLine = document.getElementById('vRefLine');
    const iARefLine = document.getElementById('iARefLine');
    const iBRefLine = document.getElementById('iBRefLine');
    const dotA = document.getElementById('dotA');
    const dotB = document.getElementById('dotB');

    // Mapping math values to SVG coords:
    // V: 0 -> 20 maps to X: 60 -> 390  (dx/dV = 330/20 = 16.5)
    // I: 0 -> 4.0 maps to Y: 210 -> 30 (dy/dI = -180/4.0 = -45)
    function updateGraph(v) {
      vDisplay.textContent = v + ' V';
      const x = 60 + v * 16.5;

      const iA = v / 5;   // Resistor A current (5 ohms)
      const iB = v / 20;  // Resistor B current (20 ohms)

      const yA = 210 - iA * 45;
      const yB = 210 - iB * 45;

      vRefLine.setAttribute('x1', x);
      vRefLine.setAttribute('x2', x);

      iARefLine.setAttribute('x2', x);
      iARefLine.setAttribute('y1', yA);
      iARefLine.setAttribute('y2', yA);

      iBRefLine.setAttribute('x2', x);
      iBRefLine.setAttribute('y1', yB);
      iBRefLine.setAttribute('y2', yB);

      dotA.setAttribute('cx', x);
      dotA.setAttribute('cy', yA);

      dotB.setAttribute('cx', x);
      dotB.setAttribute('cy', yB);
    }

    slider.addEventListener('input', (e) => {
      updateGraph(parseFloat(e.target.value));
    });

    updateGraph(10);
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="1:1">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, sans-serif;
      color: #1e2945;
      background: transparent;
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 12px;
      user-select: none;
    }
    .top-panel {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 20px;
      flex-wrap: wrap;
    }
    .triangle-box {
      width: 130px;
      height: 105px;
      position: relative;
    }
    .tri-btn {
      position: absolute;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      font-weight: 700;
      font-size: 16px;
      border-radius: 6px;
      transition: background 0.2s ease, color 0.2s ease;
      color: #1e2945;
    }
    .tri-btn.active {
      background: #2563eb;
      color: #ffffff;
    }
    .btn-v {
      top: 14px;
      left: 45px;
      width: 40px;
      height: 32px;
    }
    .btn-i {
      bottom: 8px;
      left: 16px;
      width: 42px;
      height: 34px;
    }
    .btn-r {
      bottom: 8px;
      right: 16px;
      width: 42px;
      height: 34px;
    }
    .formula-card {
      background: #f1f5f9;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 10px 16px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-width: 130px;
    }
    .formula-math {
      font-size: 22px;
      font-weight: 700;
      color: #1e2945;
      display: flex;
      align-items: center;
      gap: 6px;
    }
    .fraction {
      display: inline-flex;
      flex-direction: column;
      align-items: center;
      font-size: 18px;
      vertical-align: middle;
    }
    .frac-top {
      border-bottom: 2px solid #1e2945;
      padding: 0 4px;
      line-height: 1.1;
    }
    .frac-bot {
      padding: 0 4px;
      line-height: 1.1;
    }
    .formula-desc {
      font-size: 12px;
      color: #64748b;
      margin-top: 4px;
      font-weight: 600;
    }
    .graph-container {
      width: 100%;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 10px 12px 6px;
      display: flex;
      flex-direction: column;
      align-items: center;
    }
    .graph-title {
      font-size: 13px;
      font-weight: 700;
      color: #1e2945;
      margin-bottom: 2px;
    }
    .graph-subtitle {
      font-size: 11px;
      color: #64748b;
      margin-bottom: 6px;
    }
    svg {
      width: 100%;
      max-width: 320px;
      height: auto;
      overflow: visible;
    }
    .axis { stroke: #64748b; stroke-width: 1.5; stroke-linecap: round; }
    .grid { stroke: #e2e8f0; stroke-width: 1; stroke-dasharray: 2 2; }
    .plot-line { stroke: #2563eb; stroke-width: 3; stroke-linecap: round; }
    .axis-label { font-size: 12px; fill: #1e2945; font-weight: 600; text-anchor: middle; }
    .point { fill: #2563eb; }
  </style>
</head>
<body>

  <div class="top-panel">
    
    <div class="triangle-box">
      <svg viewBox="0 0 130 105" width="130" height="105">
        <polygon points="65,6 8,98 122,98" fill="#ffffff" stroke="#cbd5e1" stroke-width="2" />
        <line x1="28" y1="58" x2="102" y2="58" stroke="#cbd5e1" stroke-width="2" />
        <line x1="65" y1="58" x2="65" y2="98" stroke="#cbd5e1" stroke-width="2" />
      </svg>
      <div class="tri-btn btn-v" id="btnV" onclick="selectVar('V')">V</div>
      <div class="tri-btn btn-i" id="btnI" onclick="selectVar('I')">I</div>
      <div class="tri-btn btn-r active" id="btnR" onclick="selectVar('R')">R</div>
    </div>

    
    <div class="formula-card">
      <div class="formula-math" id="equationDisplay">
        <span>R</span> = 
        <div class="fraction">
          <span class="frac-top">V</span>
          <span class="frac-bot">I</span>
        </div>
      </div>
      <div class="formula-desc" id="equationLabel">Resistance = V ÷ I</div>
    </div>
  </div>

  
  <div class="graph-container">
    <div class="graph-title">Ohmic Conductor</div>
    <div class="graph-subtitle">Constant Temperature (I ∝ V)</div>
    
    <svg viewBox="0 0 280 160">
      
      <line x1="40" y1="20" x2="260" y2="20" class="grid" />
      <line x1="40" y1="55" x2="260" y2="55" class="grid" />
      <line x1="40" y1="90" x2="260" y2="90" class="grid" />
      <line x1="95" y1="20" x2="95" y2="125" class="grid" />
      <line x1="150" y1="20" x2="150" y2="125" class="grid" />
      <line x1="205" y1="20" x2="205" y2="125" class="grid" />

      
      <line x1="40" y1="125" x2="260" y2="125" class="axis" />
      <line x1="40" y1="125" x2="40" y2="15" class="axis" />

      
      <path d="M 260 122 L 265 125 L 260 128 Z" fill="#64748b" />
      <path d="M 37 15 L 40 10 L 43 15 Z" fill="#64748b" />

      
      <text x="32" y="137" font-size="11" fill="#64748b" font-weight="600">0</text>

      
      <text x="250" y="142" class="axis-label">V (V)</text>
      <text x="24" y="24" class="axis-label">I (A)</text>

      
      <line x1="40" y1="125" x2="240" y2="25" class="plot-line" />

      
      <circle cx="40" cy="125" r="3.5" class="point" />
      <circle cx="90" cy="100" r="3.5" class="point" />
      <circle cx="140" cy="75" r="3.5" class="point" />
      <circle cx="190" cy="50" r="3.5" class="point" />
      <circle cx="240" cy="25" r="3.5" class="point" />

      
      <text x="180" y="85" font-size="11" fill="#2563eb" font-weight="700">Gradient = 1 / R</text>
    </svg>
  </div>

  <script>
    function selectVar(v) {
      document.getElementById('btnV').classList.toggle('active', v === 'V');
      document.getElementById('btnI').classList.toggle('active', v === 'I');
      document.getElementById('btnR').classList.toggle('active', v === 'R');

      const eq = document.getElementById('equationDisplay');
      const lbl = document.getElementById('equationLabel');

      if (v === 'R') {
        eq.innerHTML = `<span>R</span> = <div class="fraction"><span class="frac-top">V</span><span class="frac-bot">I</span></div>`;
        lbl.textContent = 'Resistance = V ÷ I';
      } else if (v === 'V') {
        eq.innerHTML = `<span>V</span> = <span>I</span> × <span>R</span>`;
        lbl.textContent = 'Potential Diff = I × R';
      } else if (v === 'I') {
        eq.innerHTML = `<span>I</span> = <div class="fraction"><span class="frac-top">V</span><span class="frac-bot">R</span></div>`;
        lbl.textContent = 'Current = V ÷ R';
      }
    }
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
      padding: 8px 12px;
    }
    .graph-container {
      width: 100%;
      max-width: 500px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 8px;
    }
    .formula-card {
      width: 100%;
      max-width: 460px;
      background: #f8fafc;
      border: 1.5px solid #e2e8f0;
      border-radius: 10px;
      padding: 8px 12px;
      font-size: clamp(12px, 3.4vw, 14.5px);
      font-weight: 700;
      text-align: center;
      color: #1e2945;
      display: flex;
      flex-wrap: wrap;
      justify-content: center;
      align-items: center;
      gap: 4px 6px;
    }
    .val-v { color: #10b981; }
    .val-i { color: #2563eb; }
    .val-r { color: #1e2945; }
    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }
    .axis-line {
      stroke: #1e2945;
      stroke-width: 2.5;
      stroke-linecap: round;
    }
    .grid-line {
      stroke: #f1f5f9;
      stroke-width: 1.5;
    }
    .tick-label {
      font-size: 12.5px;
      fill: #64748b;
      font-weight: 500;
    }
    .axis-title {
      font-size: 13.5px;
      font-weight: 700;
      fill: #1e2945;
    }
    .plot-line {
      stroke: #1e2945;
      stroke-width: 3;
      stroke-linecap: round;
    }
    .delta-i {
      stroke: #2563eb;
      stroke-width: 2.5;
      stroke-dasharray: 6, 6;
    }
    .delta-v {
      stroke: #10b981;
      stroke-width: 2.5;
      stroke-dasharray: 6, 6;
    }
    .delta-label-i {
      fill: #2563eb;
      font-size: 13px;
      font-weight: 700;
    }
    .delta-label-v {
      fill: #10b981;
      font-size: 13px;
      font-weight: 700;
    }
    .coord-label {
      font-size: 12.5px;
      font-weight: 700;
      fill: #1e2945;
    }
  </style>
</head>
<body>

<div class="graph-container">
  
  <div class="formula-card">
    <span>Gradient = <span class="val-v">ΔV</span> / <span class="val-i">ΔI</span></span>
    <span>= <span class="val-v">6.0 V</span> / <span class="val-i">0.5 A</span></span>
    <span>= <span class="val-r">12 Ω</span></span>
  </div>

  <svg viewBox="0 0 490 330" aria-label="V-I Graph showing linear resistance calculation">
    <defs>
      <marker id="arrow-y" viewBox="0 0 10 10" refX="5" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
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      </marker>
      <marker id="arrow-x" viewBox="0 0 10 10" refX="5" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
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      </marker>
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    <line x1="190" y1="35" x2="190" y2="280" class="grid-line" />
    <line x1="250" y1="35" x2="250" y2="280" class="grid-line" />
    <line x1="310" y1="35" x2="310" y2="280" class="grid-line" />
    <line x1="370" y1="35" x2="370" y2="280" class="grid-line" />
    <line x1="430" y1="35" x2="430" y2="280" class="grid-line" />

    
    <line x1="70" y1="245" x2="440" y2="245" class="grid-line" />
    <line x1="70" y1="210" x2="440" y2="210" class="grid-line" />
    <line x1="70" y1="175" x2="440" y2="175" class="grid-line" />
    <line x1="70" y1="140" x2="440" y2="140" class="grid-line" />
    <line x1="70" y1="105" x2="440" y2="105" class="grid-line" />
    <line x1="70" y1="70" x2="440" y2="70" class="grid-line" />
    <line x1="70" y1="35" x2="440" y2="35" class="grid-line" />

    
    <polygon points="70,280 370,280 370,70" fill="#f8fafc" opacity="0.9" />

    
    <path d="M 355,280 L 355,265 L 370,265" fill="none" stroke="#94a3b8" stroke-width="1.5" />

    
    <line x1="70" y1="280" x2="370" y2="280" class="delta-i" />
    <text x="220" y="270" text-anchor="middle" class="delta-label-i">ΔI = 0.5 A</text>

    
    <line x1="370" y1="280" x2="370" y2="70" class="delta-v" />
    <text x="382" y="180" text-anchor="start" class="delta-label-v">ΔV = 6.0 V</text>

    
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    <text x="70" y="14" text-anchor="middle" class="axis-title">Voltage, V (V)</text>
    <text x="450" y="318" text-anchor="end" class="axis-title">Current, I (A)</text>

    
    <text x="70" y="298" text-anchor="middle" class="tick-label">0</text>
    <text x="130" y="298" text-anchor="middle" class="tick-label">0.1</text>
    <text x="190" y="298" text-anchor="middle" class="tick-label">0.2</text>
    <text x="250" y="298" text-anchor="middle" class="tick-label">0.3</text>
    <text x="310" y="298" text-anchor="middle" class="tick-label">0.4</text>
    <text x="370" y="298" text-anchor="middle" class="tick-label">0.5</text>

    
    <text x="58" y="284" text-anchor="end" class="tick-label">0</text>
    <text x="58" y="214" text-anchor="end" class="tick-label">2</text>
    <text x="58" y="144" text-anchor="end" class="tick-label">4</text>
    <text x="58" y="74" text-anchor="end" class="tick-label">6</text>

    
    <circle cx="70" cy="280" r="4.5" fill="#1e2945" />
    <circle cx="370" cy="70" r="5" fill="#1e2945" />
    <text x="358" y="58" text-anchor="end" class="coord-label">(0.5, 6.0)</text>
  </svg>
</div>

</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * {
      box-sizing: border-box;
      margin: 0;
      padding: 0;
    }

    body {
      width: 100%;
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8fafc;
      color: #1e293b;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      padding: 12px;
    }

    .diagram-grid {
      width: 100%;
      max-width: 660px;
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
      position: relative;
    }

    .state-card {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      position: relative;
      overflow: hidden;
    }

    .header-row {
      width: 100%;
      display: flex;
      justify-content: space-between;
      align-items: center;
      margin-bottom: 8px;
      font-size: 14px;
      font-weight: 700;
    }

    .temp-cold { color: #0284c7; }
    .temp-hot { color: #ea580c; }

    .badge {
      font-size: 11px;
      font-weight: 700;
      padding: 4px 8px;
      border-radius: 9999px;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }

    .badge-high {
      background: #fee2e2;
      color: #b91c1c;
      border: 1px solid #fca5a5;
    }

    .badge-low {
      background: #dcfce7;
      color: #15803d;
      border: 1px solid #86efac;
    }

    .svg-container {
      width: 100%;
      aspect-ratio: 1 / 1;
      max-height: 240px;
      background: #f1f5f9;
      border-radius: 8px;
      position: relative;
    }

    .hot-bg {
      background: radial-gradient(circle at center, #fff7ed 0%, #fef2f2 100%);
    }

    .transition-banner {
      grid-column: 1 / -1;
      background: #e0f2fe;
      border: 1px solid #bae6fd;
      border-radius: 8px;
      padding: 6px 12px;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      font-size: 13px;
      font-weight: 600;
      color: #0369a1;
      text-align: center;
    }

    /* SVG Elements & Keyframes */
    .ion {
      fill: #94a3b8;
      stroke: #64748b;
      stroke-width: 1.5;
    }

    .ion-label {
      font-size: 8px;
      font-weight: 700;
      fill: #ffffff;
      text-anchor: middle;
      dominant-baseline: central;
    }

    .bond {
      stroke: #cbd5e1;
      stroke-width: 2;
    }

    .bound-e {
      fill: #3b82f6;
      stroke: #1d4ed8;
      stroke-width: 0.8;
    }

    .free-e {
      fill: #00e5ff;
      filter: drop-shadow(0 0 3px #00e5ff);
    }

    .heat-wave {
      stroke: #fbbf24;
      stroke-width: 1.5;
      fill: none;
      opacity: 0.6;
      stroke-dasharray: 4 2;
      animation: heatPulse 2s infinite linear;
    }

    @keyframes heatPulse {
      0% { stroke-dashoffset: 0; opacity: 0.3; }
      50% { opacity: 0.8; }
      100% { stroke-dashoffset: -12; opacity: 0.3; }
    }

    /* Slow Drift in Cold */
    @keyframes slowDrift1 {
      0%, 100% { transform: translate(0, 0); }
      50% { transform: translate(6px, -4px); }
    }
    @keyframes slowDrift2 {
      0%, 100% { transform: translate(0, 0); }
      50% { transform: translate(-5px, 6px); }
    }
    .slow-1 { animation: slowDrift1 4s ease-in-out infinite; }
    .slow-2 { animation: slowDrift2 5s ease-in-out infinite; }

    /* Fast Motion in Hot */
    @keyframes fastZigZag1 {
      0% { transform: translate(0, 0); }
      25% { transform: translate(14px, -18px); }
      50% { transform: translate(24px, 6px); }
      75% { transform: translate(8px, 20px); }
      100% { transform: translate(0, 0); }
    }
    @keyframes fastZigZag2 {
      0% { transform: translate(0, 0); }
      25% { transform: translate(-16px, 14px); }
      50% { transform: translate(12px, 22px); }
      75% { transform: translate(-8px, -10px); }
      100% { transform: translate(0, 0); }
    }
    @keyframes fastZigZag3 {
      0% { transform: translate(0, 0); }
      25% { transform: translate(18px, 12px); }
      50% { transform: translate(-10px, -16px); }
      75% { transform: translate(-20px, 8px); }
      100% { transform: translate(0, 0); }
    }

    .fast-1 { animation: fastZigZag1 1.4s infinite ease-in-out; }
    .fast-2 { animation: fastZigZag2 1.6s infinite ease-in-out; }
    .fast-3 { animation: fastZigZag3 1.2s infinite ease-in-out; }
  </style>
</head>
<body>

  <div class="diagram-grid">
    
    <div class="state-card">
      <div class="header-row">
        <span class="temp-cold">0°C (Cold)</span>
        <span class="badge badge-high">High Resistance</span>
      </div>
      <div class="svg-container">
        <svg viewBox="0 0 200 200" width="100%" height="100%">
          
          <line x1="45" y1="45" x2="155" y2="45" class="bond" />
          <line x1="45" y1="100" x2="155" y2="100" class="bond" />
          <line x1="45" y1="155" x2="155" y2="155" class="bond" />
          <line x1="45" y1="45" x2="45" y2="155" class="bond" />
          <line x1="100" y1="45" x2="100" y2="155" class="bond" />
          <line x1="155" y1="45" x2="155" y2="155" class="bond" />

          
          
          <circle cx="70" cy="43" r="2.5" class="bound-e" />
          <circle cx="75" cy="47" r="2.5" class="bound-e" />
          <circle cx="125" cy="43" r="2.5" class="bound-e" />
          <circle cx="130" cy="47" r="2.5" class="bound-e" />

          <circle cx="70" cy="98" r="2.5" class="bound-e" />
          <circle cx="75" cy="102" r="2.5" class="bound-e" />
          <circle cx="125" cy="98" r="2.5" class="bound-e" />
          <circle cx="130" cy="102" r="2.5" class="bound-e" />

          <circle cx="70" cy="153" r="2.5" class="bound-e" />
          <circle cx="75" cy="157" r="2.5" class="bound-e" />
          <circle cx="125" cy="153" r="2.5" class="bound-e" />
          <circle cx="130" cy="157" r="2.5" class="bound-e" />

          
          <circle cx="43" cy="70" r="2.5" class="bound-e" />
          <circle cx="47" cy="75" r="2.5" class="bound-e" />
          <circle cx="43" cy="125" r="2.5" class="bound-e" />
          <circle cx="47" cy="130" r="2.5" class="bound-e" />

          <circle cx="98" cy="70" r="2.5" class="bound-e" />
          <circle cx="102" cy="75" r="2.5" class="bound-e" />
          <circle cx="98" cy="125" r="2.5" class="bound-e" />
          <circle cx="102" cy="130" r="2.5" class="bound-e" />

          <circle cx="153" cy="70" r="2.5" class="bound-e" />
          <circle cx="157" cy="75" r="2.5" class="bound-e" />
          <circle cx="153" cy="125" r="2.5" class="bound-e" />
          <circle cx="157" cy="130" r="2.5" class="bound-e" />

          
          <g>
            <circle cx="45" cy="45" r="10" class="ion" />
            <text x="45" y="45" class="ion-label">+</text>

            <circle cx="100" cy="45" r="10" class="ion" />
            <text x="100" y="45" class="ion-label">+</text>

            <circle cx="155" cy="45" r="10" class="ion" />
            <text x="155" y="45" class="ion-label">+</text>

            <circle cx="45" cy="100" r="10" class="ion" />
            <text x="45" y="100" class="ion-label">+</text>

            <circle cx="100" cy="100" r="10" class="ion" />
            <text x="100" y="100" class="ion-label">+</text>

            <circle cx="155" cy="100" r="10" class="ion" />
            <text x="155" y="100" class="ion-label">+</text>

            <circle cx="45" cy="155" r="10" class="ion" />
            <text x="45" y="155" class="ion-label">+</text>

            <circle cx="100" cy="155" r="10" class="ion" />
            <text x="100" y="155" class="ion-label">+</text>

            <circle cx="155" cy="155" r="10" class="ion" />
            <text x="155" y="155" class="ion-label">+</text>
          </g>

          
          <circle cx="135" cy="75" r="3.5" class="free-e slow-1" />
          <circle cx="68" cy="132" r="3.5" class="free-e slow-2" />
        </svg>
      </div>
    </div>

    
    <div class="state-card">
      <div class="header-row">
        <span class="temp-hot">80°C (Hot)</span>
        <span class="badge badge-low">Low Resistance</span>
      </div>
      <div class="svg-container hot-bg">
        <svg viewBox="0 0 200 200" width="100%" height="100%">
          
          <path d="M 20,30 Q 30,20 40,30 T 60,30 T 80,30" class="heat-wave" />
          <path d="M 120,40 Q 130,30 140,40 T 160,40 T 180,40" class="heat-wave" />
          <path d="M 20,175 Q 30,165 40,175 T 60,175 T 80,175" class="heat-wave" />
          <path d="M 120,170 Q 130,160 140,170 T 160,170 T 180,170" class="heat-wave" />

          
          <line x1="45" y1="45" x2="155" y2="45" class="bond" stroke-dasharray="8 6" />
          <line x1="45" y1="100" x2="155" y2="100" class="bond" stroke-dasharray="6 8" />
          <line x1="45" y1="155" x2="155" y2="155" class="bond" stroke-dasharray="8 6" />
          <line x1="45" y1="45" x2="45" y2="155" class="bond" stroke-dasharray="6 8" />
          <line x1="100" y1="45" x2="100" y2="155" class="bond" stroke-dasharray="8 6" />
          <line x1="155" y1="45" x2="155" y2="155" class="bond" stroke-dasharray="6 8" />

          
          <g>
            <circle cx="45" cy="45" r="10" class="ion" />
            <text x="45" y="45" class="ion-label">+</text>

            <circle cx="100" cy="45" r="10" class="ion" />
            <text x="100" y="45" class="ion-label">+</text>

            <circle cx="155" cy="45" r="10" class="ion" />
            <text x="155" y="45" class="ion-label">+</text>

            <circle cx="45" cy="100" r="10" class="ion" />
            <text x="45" y="100" class="ion-label">+</text>

            <circle cx="100" cy="100" r="10" class="ion" />
            <text x="100" y="100" class="ion-label">+</text>

            <circle cx="155" cy="100" r="10" class="ion" />
            <text x="155" y="100" class="ion-label">+</text>

            <circle cx="45" cy="155" r="10" class="ion" />
            <text x="45" y="155" class="ion-label">+</text>

            <circle cx="100" cy="155" r="10" class="ion" />
            <text x="100" y="155" class="ion-label">+</text>

            <circle cx="155" cy="155" r="10" class="ion" />
            <text x="155" y="155" class="ion-label">+</text>
          </g>

          
          <circle cx="70" cy="40" r="3.5" class="free-e fast-1" />
          <circle cx="130" cy="46" r="3.5" class="free-e fast-2" />
          <circle cx="42" cy="74" r="3.5" class="free-e fast-3" />
          <circle cx="76" cy="72" r="3.5" class="free-e fast-2" />
          <circle cx="120" cy="75" r="3.5" class="free-e fast-1" />
          <circle cx="160" cy="72" r="3.5" class="free-e fast-3" />

          <circle cx="72" cy="100" r="3.5" class="free-e fast-3" />
          <circle cx="128" cy="102" r="3.5" class="free-e fast-1" />

          <circle cx="42" cy="126" r="3.5" class="free-e fast-2" />
          <circle cx="78" cy="128" r="3.5" class="free-e fast-1" />
          <circle cx="122" cy="124" r="3.5" class="free-e fast-3" />
          <circle cx="160" cy="128" r="3.5" class="free-e fast-2" />

          <circle cx="72" cy="156" r="3.5" class="free-e fast-1" />
          <circle cx="126" cy="154" r="3.5" class="free-e fast-2" />

          <circle cx="100" cy="18" r="3.5" class="free-e fast-3" />
          <circle cx="100" cy="182" r="3.5" class="free-e fast-1" />
        </svg>
      </div>
    </div>

    
    <div class="transition-banner">
      <span>Thermal energy releases free charge carriers</span>
      <span>➔</span>
    </div>
  </div>

</body>
</html>

Thermistors: Temperature-Dependent Resistance Behaviour

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Thermistor Resistance vs Temperature (NTC)</title>
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      color: #1e293b;
      background: transparent;
      user-select: none;
      -webkit-user-select: none;
      display: flex;
      flex-direction: column;
      align-items: center;
      padding: 10px 12px;
      gap: 10px;
      width: 100%;
      max-width: 540px;
      margin: 0 auto;
    }

    .header-panel {
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 6px;
      width: 100%;
    }

    .preset-row {
      display: flex;
      flex-wrap: wrap;
      justify-content: center;
      gap: 6px;
      width: 100%;
    }

    .preset-btn {
      padding: 5px 12px;
      font-size: 12px;
      font-weight: 600;
      border: 1.5px solid #cbd5e1;
      border-radius: 6px;
      background: #ffffff;
      color: #334155;
      cursor: pointer;
      box-shadow: 0 1px 2px rgba(0,0,0,0.04);
      transition: background 0.15s, border-color 0.15s, color 0.15s;
    }

    .preset-btn:hover {
      background: #f8fafc;
      border-color: #94a3b8;
    }

    .preset-btn.active {
      background: #eff6ff;
      border-color: #2563eb;
      color: #1d4ed8;
      box-shadow: 0 0 0 1px #2563eb;
    }

    .graph-container {
      position: relative;
      width: 100%;
      aspect-ratio: 4 / 3;
      touch-action: none;
      cursor: crosshair;
    }

    svg {
      width: 100%;
      height: 100%;
      display: block;
      overflow: visible;
    }

    .axis-line { stroke: #64748b; stroke-width: 1.5; }
    .grid-line { stroke: #e2e8f0; stroke-width: 1; }
    .grid-line-major { stroke: #cbd5e1; stroke-width: 1; stroke-dasharray: 2 2; }
    .tick-label { font-size: 11px; fill: #64748b; font-family: inherit; font-weight: 500; }
    .axis-title { font-size: 12px; fill: #0f172a; font-weight: 700; }

    .curve-path {
      fill: none;
      stroke: #2563eb;
      stroke-width: 3.5;
      stroke-linecap: round;
      stroke-linejoin: round;
    }

    .key-point {
      fill: #ffffff;
      stroke: #2563eb;
      stroke-width: 2.5;
      cursor: pointer;
      transition: stroke-width 0.15s ease;
    }

    .key-point:hover {
      stroke-width: 3.5;
      stroke: #1d4ed8;
    }

    .point-label { font-size: 11px; font-weight: 700; fill: #0f172a; pointer-events: none; }
    .point-sub { font-size: 10px; font-weight: 500; fill: #475569; pointer-events: none; }

    .interactive-marker {
      fill: #ef4444;
      stroke: #ffffff;
      stroke-width: 2.5;
      filter: drop-shadow(0 2px 4px rgba(0,0,0,0.25));
      pointer-events: none;
    }

    .readout-box {
      fill: #0f172a;
      stroke: #334155;
      stroke-width: 1;
      rx: 6;
      filter: drop-shadow(0 3px 6px rgba(0,0,0,0.18));
      pointer-events: none;
    }

    .instruction-note {
      font-size: 11px;
      color: #64748b;
      text-align: center;
      margin-top: -2px;
    }
  </style>
</head>
<body>

  <div class="header-panel">
    <div class="preset-row">
      <button class="preset-btn active" onclick="setTemp(0)">❄️ Freezing (0°C)</button>
      <button class="preset-btn" onclick="setTemp(25)">🏠 Room (25°C)</button>
      <button class="preset-btn" onclick="setTemp(100)">🔥 Boiling (100°C)</button>
    </div>
  </div>

  <div class="graph-container" id="graphArea">
    <svg viewBox="0 0 440 330" id="graphSvg">
      
      <g id="grid">
        <line x1="55" y1="260" x2="395" y2="260" class="grid-line" />
        <line x1="55" y1="218" x2="395" y2="218" class="grid-line" />
        <line x1="55" y1="176" x2="395" y2="176" class="grid-line" />
        <line x1="55" y1="134" x2="395" y2="134" class="grid-line" />
        <line x1="55" y1="92" x2="395" y2="92" class="grid-line" />
        <line x1="55" y1="50" x2="395" y2="50" class="grid-line" />

        <line x1="55" y1="40" x2="55" y2="260" class="grid-line" />
        <line x1="140" y1="40" x2="140" y2="260" class="grid-line" />
        <line x1="225" y1="40" x2="225" y2="260" class="grid-line" />
        <line x1="310" y1="40" x2="310" y2="260" class="grid-line" />
        <line x1="395" y1="40" x2="395" y2="260" class="grid-line" />
      </g>

      
      <line x1="55" y1="260" x2="405" y2="260" class="axis-line" />
      <line x1="55" y1="35" x2="55" y2="260" class="axis-line" />

      
      <text x="46" y="264" text-anchor="end" class="tick-label">0</text>
      <text x="46" y="222" text-anchor="end" class="tick-label">2</text>
      <text x="46" y="180" text-anchor="end" class="tick-label">4</text>
      <text x="46" y="138" text-anchor="end" class="tick-label">6</text>
      <text x="46" y="96" text-anchor="end" class="tick-label">8</text>
      <text x="46" y="54" text-anchor="end" class="tick-label">10</text>

      <text x="16" y="20" class="axis-title" transform="rotate(-90 16,20)" text-anchor="end">Resistance R (kΩ)</text>

      
      <text x="55" y="278" text-anchor="middle" class="tick-label">0</text>
      <text x="140" y="278" text-anchor="middle" class="tick-label">25</text>
      <text x="225" y="278" text-anchor="middle" class="tick-label">50</text>
      <text x="310" y="278" text-anchor="middle" class="tick-label">75</text>
      <text x="395" y="278" text-anchor="middle" class="tick-label">100</text>

      <text x="225" y="304" text-anchor="middle" class="axis-title">Temperature T (°C)</text>

      
      <path id="thermistorCurve" class="curve-path" />

      
      <line id="projX" x1="0" y1="0" x2="0" y2="0" stroke="#ef4444" stroke-dasharray="3 3" stroke-width="1.3" opacity="0.75" />
      <line id="projY" x1="0" y1="0" x2="0" y2="0" stroke="#ef4444" stroke-dasharray="3 3" stroke-width="1.3" opacity="0.75" />

      
      
      <g style="cursor: pointer;" onclick="setTemp(0)">
        <circle cx="55" cy="50" r="5" class="key-point" />
        <text x="68" y="28" class="point-label">Freezing</text>
        <text x="68" y="41" class="point-sub">0°C, 10 kΩ</text>
      </g>

      
      <g style="cursor: pointer;" onclick="setTemp(25)">
        <circle cx="140" cy="218" r="5" class="key-point" />
        <text x="154" y="178" class="point-label">Room Temp</text>
        <text x="154" y="191" class="point-sub">25°C, 2 kΩ</text>
      </g>

      
      <g style="cursor: pointer;" onclick="setTemp(100)">
        <circle cx="395" cy="255.8" r="5" class="key-point" />
        <text x="392" y="222" text-anchor="end" class="point-label">Boiling</text>
        <text x="392" y="235" text-anchor="end" class="point-sub">100°C, 0.2 kΩ</text>
      </g>

      
      <circle id="activeDot" cx="55" cy="50" r="6" class="interactive-marker" />

      
      <g id="tooltipGroup" transform="translate(130, 85)">
        <rect id="tooltipRect" x="-52" y="-14" width="104" height="26" class="readout-box" />
        <text id="tooltipText" x="0" y="3.5" text-anchor="middle" font-size="11" font-weight="700" fill="#ffffff">0°C, 10.0 kΩ</text>
      </g>
    </svg>
  </div>

  <p class="instruction-note">Drag along the curve or tap presets to inspect temperature vs resistance</p>

  <script>
    // Exact thermistor curve model:
    // Fits R(0)=10, R(25)=2, R(100)=0.2 smoothly
    function calcR(T) {
      if (T <= 0) return 10.0;
      if (T >= 100) return 0.2;
      return Math.exp(2.302585093 - 0.072796612 * T + 0.000336764 * T * T);
    }

    const xMin = 55, xMax = 395;
    const yMin = 50, yZero = 260; // 10 kΩ -> y=50, 0 kΩ -> y=260 (21 px per kΩ)

    function getCoords(T) {
      const R = calcR(T);
      const x = xMin + (T / 100) * (xMax - xMin);
      const y = yZero - (R / 10) * (yZero - yMin);
      return { x, y, R };
    }

    // Build SVG Path starting exactly at (0°C, 10 kΩ) -> (55, 50)
    let pathData = `M 55.00 50.00`;
    for (let t = 0.5; t <= 100; t += 0.5) {
      const { x, y } = getCoords(t);
      pathData += ` L ${x.toFixed(2)} ${y.toFixed(2)}`;
    }
    // Guarantee it terminates precisely at (100, 0.2)
    pathData += ` L 395.00 255.80`;
    document.getElementById('thermistorCurve').setAttribute('d', pathData);

    const activeDot = document.getElementById('activeDot');
    const projX = document.getElementById('projX');
    const projY = document.getElementById('projY');
    const tooltipGroup = document.getElementById('tooltipGroup');
    const tooltipText = document.getElementById('tooltipText');
    const buttons = document.querySelectorAll('.preset-btn');

    let currentT = 0;

    function updateDisplay(T) {
      currentT = Math.max(0, Math.min(100, T));
      const { x, y, R } = getCoords(currentT);

      activeDot.setAttribute('cx', x);
      activeDot.setAttribute('cy', y);

      projX.setAttribute('x1', x);
      projX.setAttribute('y1', y);
      projX.setAttribute('x2', x);
      projX.setAttribute('y2', yZero);

      projY.setAttribute('x1', xMin);
      projY.setAttribute('y1', y);
      projY.setAttribute('x2', x);
      projY.setAttribute('y2', y);

      const rText = R >= 1 ? R.toFixed(1) : R.toFixed(2);
      const tText = currentT.toFixed(0);
      tooltipText.textContent = `${tText}°C, ${rText} kΩ`;

      // Smart positioning of tooltip that guarantees no overlap with static point labels:
      // - At T < 20 (near Freezing): place tooltip below and right of the marker
      // - At 20 <= T < 70 (mid curve): place tooltip above the curve
      // - At T >= 70 (near Boiling): place tooltip to the left of the marker
      let tipX, tipY;
      if (currentT < 18) {
        tipX = x + 65;
        tipY = y + 42;
      } else if (currentT < 70) {
        tipX = x;
        tipY = y - 28;
      } else {
        tipX = Math.min(320, x - 55);
        tipY = y - 28;
      }

      tooltipGroup.setAttribute('transform', `translate(${tipX.toFixed(1)}, ${tipY.toFixed(1)})`);

      // Update preset buttons state
      buttons[0].classList.toggle('active', Math.abs(currentT - 0) < 1.5);
      buttons[1].classList.toggle('active', Math.abs(currentT - 25) < 1.5);
      buttons[2].classList.toggle('active', Math.abs(currentT - 100) < 1.5);
    }

    function setTemp(t) {
      updateDisplay(t);
    }

    // Drag / Touch Interaction
    const container = document.getElementById('graphArea');
    const svg = document.getElementById('graphSvg');
    let isDragging = false;

    function handlePointer(e) {
      const rect = svg.getBoundingClientRect();
      const clientX = e.clientX ?? (e.touches && e.touches[0].clientX);
      if (clientX === undefined) return;
      const svgX = ((clientX - rect.left) / rect.width) * 440;
      const clampedX = Math.max(xMin, Math.min(xMax, svgX));
      const T = ((clampedX - xMin) / (xMax - xMin)) * 100;
      updateDisplay(T);
    }

    container.addEventListener('pointerdown', (e) => {
      isDragging = true;
      handlePointer(e);
      try { container.setPointerCapture(e.pointerId); } catch(err) {}
    });

    container.addEventListener('pointermove', (e) => {
      if (isDragging) handlePointer(e);
    });

    container.addEventListener('pointerup', (e) => {
      isDragging = false;
      try { container.releasePointerCapture(e.pointerId); } catch(err) {}
    });

    container.addEventListener('pointercancel', () => {
      isDragging = false;
    });

    // Initial render at Freezing (0°C)
    updateDisplay(0);
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <title>NTC Thermistor Characteristics</title>
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif; }
    body {
      background: #ffffff;
      color: #1e293b;
      padding: 10px;
      display: flex;
      flex-direction: column;
      gap: 8px;
      user-select: none;
    }

    /* Header & Symbol Bar */
    .header-bar {
      display: flex;
      align-items: center;
      justify-content: space-between;
      flex-wrap: wrap;
      gap: 6px;
    }
    .title-group {
      display: flex;
      align-items: center;
      gap: 6px;
    }
    .badge {
      background: #eff6ff;
      color: #0284c7;
      border: 1px solid #bfdbfe;
      font-size: 11px;
      font-weight: 700;
      padding: 2px 8px;
      border-radius: 12px;
      letter-spacing: 0.2px;
    }
    .rule-badge {
      background: #f0fdf4;
      color: #166534;
      border: 1px solid #bbf7d0;
      font-size: 11px;
      font-weight: 700;
      padding: 2px 8px;
      border-radius: 12px;
    }

    /* Main Grid Layout */
    .grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 8px;
    }
    @media (max-width: 480px) {
      .grid {
        grid-template-columns: 1fr;
      }
    }

    .card-panel {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      padding: 8px 10px;
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    /* Symbol & Circuit Mini-view */
    .symbol-row {
      display: flex;
      align-items: center;
      justify-content: space-between;
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 4px 10px;
    }
    .symbol-label {
      font-size: 11px;
      font-weight: 600;
      color: #64748b;
    }

    /* Thermal Controls */
    .thermo-control {
      display: flex;
      align-items: center;
      gap: 10px;
    }
    .thermo-graphic {
      width: 24px;
      height: 76px;
      background: #e2e8f0;
      border-radius: 12px;
      position: relative;
      overflow: hidden;
      border: 1.5px solid #cbd5e1;
      flex-shrink: 0;
    }
    .thermo-fluid {
      position: absolute;
      bottom: 0;
      left: 0;
      right: 0;
      background: #0284c7;
      border-radius: 0 0 10px 10px;
      transition: height 0.15s ease, background-color 0.15s ease;
    }
    .thermo-slider-box {
      flex: 1;
      display: flex;
      flex-direction: column;
      gap: 4px;
    }
    .val-display {
      font-size: 16px;
      font-weight: 700;
      color: #0f172a;
      display: flex;
      justify-content: space-between;
      align-items: baseline;
    }
    .val-display span {
      font-size: 11px;
      color: #64748b;
      font-weight: 600;
    }

    input[type=range] {
      -webkit-appearance: none;
      width: 100%;
      height: 6px;
      border-radius: 3px;
      background: #cbd5e1;
      outline: none;
      cursor: pointer;
    }
    input[type=range]::-webkit-slider-thumb {
      -webkit-appearance: none;
      width: 18px;
      height: 18px;
      border-radius: 50%;
      background: #0284c7;
      border: 2px solid #ffffff;
      box-shadow: 0 1px 3px rgba(0,0,0,0.3);
      cursor: pointer;
    }

    /* Preset Buttons */
    .presets {
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 4px;
    }
    .preset-btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      border-radius: 6px;
      padding: 4px 2px;
      font-size: 10px;
      font-weight: 600;
      color: #334155;
      cursor: pointer;
      text-align: center;
      line-height: 1.2;
    }
    .preset-btn.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
    }

    /* Meter Display */
    .lcd-screen {
      background: #f1f5f9;
      border: 1.5px solid #cbd5e1;
      border-radius: 8px;
      padding: 6px 10px;
      display: flex;
      justify-content: space-between;
      align-items: center;
    }
    .lcd-text {
      font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
      font-size: 20px;
      font-weight: 700;
      color: #0f172a;
      letter-spacing: 0.5px;
    }
    .lcd-unit {
      font-size: 12px;
      font-weight: 700;
      color: #64748b;
    }

    /* Graph Container */
    .graph-container {
      width: 100%;
      height: 100px;
      position: relative;
    }
    svg.graph-svg {
      width: 100%;
      height: 100%;
      overflow: visible;
    }
  </style>
</head>
<body>

  
  <div class="header-bar">
    <div class="title-group">
      <span class="badge">NTC Thermistor</span>
    </div>
    <span class="rule-badge">Temp ↑ ⇒ Resistance ↓</span>
  </div>

  
  <div class="symbol-row">
    <span class="symbol-label">IEC Circuit Symbol:</span>
    <svg width="110" height="24" viewBox="0 0 110 24">
      
      <line x1="5" y1="12" x2="30" y2="12" stroke="#1e293b" stroke-width="2" />
      <line x1="80" y1="12" x2="105" y2="12" stroke="#1e293b" stroke-width="2" />
      
      <rect x="30" y="5" width="50" height="14" fill="#ffffff" stroke="#1e293b" stroke-width="2" />
      
      <path d="M 22 21 L 32 21 L 88 3" fill="none" stroke="#0284c7" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" />
      
      <circle cx="5" cy="12" r="2.5" fill="#1e293b" />
      <circle cx="105" cy="12" r="2.5" fill="#1e293b" />
    </svg>
  </div>

  
  <div class="grid">
    
    <div class="card-panel">
      <div class="val-display">
        <div><span id="tempVal">20</span>°C</div>
        <span>Temperature (T)</span>
      </div>

      <div class="thermo-control">
        <div class="thermo-graphic">
          <div class="thermo-fluid" id="thermoFluid" style="height: 20%; background: #0284c7;"></div>
        </div>
        <div class="thermo-slider-box">
          <input type="range" id="tempSlider" min="0" max="100" value="20" step="1">
          <div class="presets">
            <button class="preset-btn" data-t="0">0°C<br>Ice</button>
            <button class="preset-btn active" data-t="20">20°C<br>Room</button>
            <button class="preset-btn" data-t="37">37°C<br>Body</button>
            <button class="preset-btn" data-t="100">100°C<br>Boil</button>
          </div>
        </div>
      </div>
    </div>

    
    <div class="card-panel">
      <div class="lcd-screen">
        <div class="lcd-text" id="resVal">4.00 kΩ</div>
        <div class="lcd-unit">Resistance (R)</div>
      </div>

      
      <div class="graph-container">
        <svg class="graph-svg" id="graphSvg" viewBox="0 0 160 80">
          
          <line x1="25" y1="5" x2="155" y2="5" stroke="#e2e8f0" stroke-width="0.8" stroke-dasharray="2,2"/>
          <line x1="25" y1="38" x2="155" y2="38" stroke="#e2e8f0" stroke-width="0.8" stroke-dasharray="2,2"/>
          <line x1="25" y1="70" x2="155" y2="70" stroke="#cbd5e1" stroke-width="1.2"/>
          <line x1="25" y1="5" x2="25" y2="70" stroke="#cbd5e1" stroke-width="1.2"/>

          
          <text x="22" y="10" fill="#64748b" font-size="7" font-weight="700" text-anchor="end">10k</text>
          <text x="22" y="70" fill="#64748b" font-size="7" font-weight="700" text-anchor="end">0</text>
          <text x="25" y="78" fill="#64748b" font-size="7" font-weight="700" text-anchor="start">0°C</text>
          <text x="155" y="78" fill="#64748b" font-size="7" font-weight="700" text-anchor="end">100°C</text>

          
          <path id="curvePath" d="" fill="none" stroke="#94a3b8" stroke-width="2" stroke-linecap="round"/>

          
          <circle id="markerDot" cx="25" cy="5" r="4.5" fill="#0284c7" stroke="#ffffff" stroke-width="1.5" />
        </svg>
      </div>
    </div>
  </div>

  <script>
    // Physics NTC model: R(T) = R0 * exp(B * (1/T - 1/T0))
    // T0 = 20°C (293.15 K), R0 = 4000 Ω, B = 3665 K
    const T0 = 293.15;
    const R0 = 4000;
    const B = 3665;

    function getResistance(tCelsius) {
      const T = tCelsius + 273.15;
      return R0 * Math.exp(B * (1 / T - 1 / T0));
    }

    // Graph plotting bounds
    const gxMin = 25, gxMax = 155;
    const gyMax = 70, gyMin = 8; // gyMin corresponds to 10kΩ
    const R_MAX_SCALE = 10000;

    function tempToX(t) {
      return gxMin + (t / 100) * (gxMax - gxMin);
    }

    function resToY(r) {
      const clampedR = Math.max(0, Math.min(R_MAX_SCALE, r));
      return gyMax - (clampedR / R_MAX_SCALE) * (gyMax - gyMin);
    }

    // Pre-calculate mathematically accurate SVG path
    function buildCurve() {
      let d = "";
      for (let t = 0; t <= 100; t += 2) {
        const r = getResistance(t);
        const x = tempToX(t);
        const y = resToY(r);
        d += (t === 0 ? `M ${x.toFixed(1)} ${y.toFixed(1)}` : ` L ${x.toFixed(1)} ${y.toFixed(1)}`);
      }
      document.getElementById('curvePath').setAttribute('d', d);
    }

    // Color gradient calculation between Cyan (#0284c7) and Red (#ef4444)
    function getTempColor(t) {
      const ratio = t / 100;
      const r = Math.round(2 + ratio * (239 - 2));
      const g = Math.round(132 - ratio * (132 - 68));
      const b = Math.round(199 - ratio * (199 - 68));
      return `rgb(${r}, ${g}, ${b})`;
    }

    const slider = document.getElementById('tempSlider');
    const tempVal = document.getElementById('tempVal');
    const resVal = document.getElementById('resVal');
    const thermoFluid = document.getElementById('thermoFluid');
    const markerDot = document.getElementById('markerDot');
    const presetBtns = document.querySelectorAll('.preset-btn');

    function updateState(t) {
      t = Math.max(0, Math.min(100, Number(t)));
      slider.value = t;
      tempVal.textContent = t;

      // Thermometer Fluid UI
      const color = getTempColor(t);
      thermoFluid.style.height = `${Math.max(8, t)}%`;
      thermoFluid.style.backgroundColor = color;

      // Resistance Calculation
      const r = getResistance(t);
      if (r >= 1000) {
        resVal.textContent = (r / 1000).toFixed(2) + " kΩ";
      } else {
        resVal.textContent = Math.round(r) + " Ω";
      }

      // Graph Dot Position
      const x = tempToX(t);
      const y = resToY(r);
      markerDot.setAttribute('cx', x.toFixed(1));
      markerDot.setAttribute('cy', y.toFixed(1));
      markerDot.setAttribute('fill', color);

      // Preset button active state
      presetBtns.forEach(btn => {
        btn.classList.toggle('active', Number(btn.dataset.t) === t);
      });
    }

    slider.addEventListener('input', (e) => updateState(e.target.value));

    presetBtns.forEach(btn => {
      btn.addEventListener('click', () => updateState(Number(btn.dataset.t)));
    });

    // Init
    buildCurve();
    updateState(20);
  </script>
</body>
</html>

UK-GCSE-SCIENCE-PHYS-ELE-05-02

Aligned learning resources

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