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Override for the tutor's lesson content generation calls. Auto uses the system default (Claude Sonnet 5 for lesson text, Opus 5 for diagrams).

Lesson generation model

System default

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Tutoring abilities

Look around your room right now. Some devices plug straight into the wall, while others run smoothly in your backpack on the playground.

Both need **electricity**—a type of energy made by the movement of tiny electric charges—to work, but they get it from two totally different sources.

<!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: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    }

    body {
      background: #f8f9fa;
      color: #1e2945;
      padding: 12px;
      min-height: 100%;
      display: flex;
      flex-direction: column;
      justify-content: center;
    }

    .comparison-grid {
      display: grid;
      grid-template-columns: repeat(2, 1fr);
      gap: 12px;
      width: 100%;
      max-width: 600px;
      margin: 0 auto;
    }

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

    .tile {
      background: #ffffff;
      border: 1.5px solid #e2e8f0;
      border-radius: 12px;
      padding: 14px 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
      cursor: pointer;
      user-select: none;
      transition: border-color 0.2s ease, box-shadow 0.2s ease;
      position: relative;
    }

    .tile:active {
      transform: translateY(1px);
    }

    .tile-title {
      font-size: 15px;
      font-weight: 700;
      margin-bottom: 8px;
    }

    .badge {
      display: inline-flex;
      align-items: center;
      gap: 4px;
      padding: 4px 10px;
      border-radius: 20px;
      font-size: 12px;
      font-weight: 600;
      margin-top: 10px;
    }

    .badge-battery {
      background: #e6f9ed;
      color: #15803d;
      border: 1px solid #bbf7d0;
    }

    .badge-mains {
      background: #fef2f2;
      color: #b91c1c;
      border: 1px solid #fecaca;
    }

    .scene-area {
      width: 100%;
      height: 150px;
      display: flex;
      align-items: center;
      justify-content: center;
      position: relative;
    }

    svg {
      overflow: visible;
    }

    .beam {
      transition: opacity 0.25s ease;
    }

    .power-glow {
      transition: opacity 0.25s ease;
    }

    .tap-hint {
      font-size: 11px;
      color: #64748b;
      margin-top: 4px;
    }
  </style>
</head>
<body>

  <div class="comparison-grid">
    
    <div class="tile" id="batteryCard" onclick="toggleBattery()">
      <div class="tile-title" style="color: #0284c7;">Battery Powered</div>
      
      <div class="scene-area">
        <svg width="140" height="130" viewBox="0 0 140 130">
          
          <polygon id="lightBeam" class="beam" points="40,46 0,20 0,90 40,64" fill="url(#beamGrad)" opacity="1" />
          
          <defs>
            <linearGradient id="beamGrad" x1="100%" y1="50%" x2="0%" y2="50%">
              <stop offset="0%" stop-color="#facc15" stop-opacity="0.7"/>
              <stop offset="100%" stop-color="#facc15" stop-opacity="0"/>
            </linearGradient>
            <linearGradient id="batteryGrad" x1="0%" y1="0%" x2="0%" y2="100%">
              <stop offset="0%" stop-color="#fbbf24"/>
              <stop offset="100%" stop-color="#d97706"/>
            </linearGradient>
          </defs>

          
          <path d="M 40 45 L 60 49 L 60 61 L 40 65 Z" fill="#eab308" stroke="#ca8a04" stroke-width="1.5" />
          <ellipse cx="40" cy="55" rx="3" ry="10" fill="#fef08a" stroke="#ca8a04" stroke-width="1.5" />

          
          <rect x="60" y="49" width="48" height="12" rx="2" fill="#facc15" stroke="#ca8a04" stroke-width="1.5" />
          <rect x="66" y="47" width="10" height="2" rx="1" fill="#475569" />

          
          <g id="batteryGroup" transform="translate(0, 32)">
            
            <rect x="106" y="66" width="3" height="4" rx="1" fill="#94a3b8" />
            
            <rect x="62" y="63" width="44" height="10" rx="2" fill="url(#batteryGrad)" stroke="#b45309" stroke-width="1" />
            <rect x="62" y="63" width="12" height="10" rx="1" fill="#1e293b" />
            <text x="82" y="71" font-size="6.5" font-weight="bold" fill="#ffffff" text-anchor="middle">1.5V AA</text>
            <text x="68" y="71" font-size="7" font-weight="bold" fill="#ffffff" text-anchor="middle">-</text>
            <text x="101" y="71" font-size="7" font-weight="bold" fill="#ffffff" text-anchor="middle">+</text>
          </g>

          
          <circle id="switchDot" cx="71" cy="48" r="2" fill="#22c55e" />
        </svg>
      </div>

      <div class="badge badge-battery">
        <span>🔋</span> 1.5V · Safe &amp; Portable
      </div>
      <div class="tap-hint" id="batteryHint">Tap to disconnect</div>
    </div>

    
    <div class="tile" id="mainsCard" onclick="toggleMains()">
      <div class="tile-title" style="color: #e11d48;">Mains Powered</div>
      
      <div class="scene-area">
        <svg width="140" height="130" viewBox="0 0 140 130">
          <defs>
            <linearGradient id="fridgeGrad" x1="0%" y1="0%" x2="100%" y2="0%">
              <stop offset="0%" stop-color="#f1f5f9"/>
              <stop offset="50%" stop-color="#e2e8f0"/>
              <stop offset="100%" stop-color="#cbd5e1"/>
            </linearGradient>
          </defs>

          
          <rect x="18" y="16" width="56" height="96" rx="5" fill="url(#fridgeGrad)" stroke="#94a3b8" stroke-width="1.5" />
          
          
          <line x1="18" y1="50" x2="74" y2="50" stroke="#94a3b8" stroke-width="1.5" />
          
          
          <rect x="22" y="32" width="3" height="12" rx="1.5" fill="#64748b" />
          <rect x="22" y="56" width="3" height="20" rx="1.5" fill="#64748b" />

          
          <circle id="fridgeGlow" class="power-glow" cx="64" cy="24" r="3" fill="#38bdf8" opacity="1" />
          <text id="snowIcon" class="power-glow" x="46" y="80" font-size="14" text-anchor="middle" fill="#0284c7" opacity="1">❄️</text>

          
          
          <rect x="112" y="70" width="18" height="24" rx="3" fill="#ffffff" stroke="#94a3b8" stroke-width="1.5" />
          <circle cx="118" cy="79" r="1.5" fill="#334155" />
          <circle cx="124" cy="79" r="1.5" fill="#334155" />
          <rect x="120" y="85" width="2" height="4" fill="#334155" />

          
          <path id="cordLine" d="M 68 95 C 90 108 95 82 110 82" fill="none" stroke="#334155" stroke-width="3" stroke-linecap="round" />
          
          
          <g id="plugHead" transform="translate(110, 77)">
            <rect x="0" y="1" width="6" height="8" rx="1.5" fill="#1e293b" />
            <rect x="6" y="3" width="3" height="1.5" fill="#fbbf24" />
            <rect x="6" y="6.5" width="3" height="1.5" fill="#fbbf24" />
          </g>

          
          <path id="spark" class="power-glow" d="M 104 68 L 107 72 L 103 74 L 108 78" fill="none" stroke="#eab308" stroke-width="1.5" stroke-linecap="round" opacity="1" />
        </svg>
      </div>

      <div class="badge badge-mains">
        <span>⚡</span> 120V · High Power
      </div>
      <div class="tap-hint" id="mainsHint">Tap to unplug</div>
    </div>
  </div>

  <script>
    let batteryOn = true;
    let mainsOn = true;

    function toggleBattery() {
      batteryOn = !batteryOn;
      const beam = document.getElementById('lightBeam');
      const dot = document.getElementById('switchDot');
      const bat = document.getElementById('batteryGroup');
      const hint = document.getElementById('batteryHint');

      if (batteryOn) {
        beam.style.opacity = '1';
        dot.setAttribute('fill', '#22c55e');
        bat.setAttribute('transform', 'translate(0, 32)');
        hint.textContent = 'Tap to disconnect';
      } else {
        beam.style.opacity = '0';
        dot.setAttribute('fill', '#94a3b8');
        bat.setAttribute('transform', 'translate(0, 48)');
        hint.textContent = 'Tap to insert battery';
      }
    }

    function toggleMains() {
      mainsOn = !mainsOn;
      const glow = document.getElementById('fridgeGlow');
      const snow = document.getElementById('snowIcon');
      const spark = document.getElementById('spark');
      const plug = document.getElementById('plugHead');
      const cord = document.getElementById('cordLine');
      const hint = document.getElementById('mainsHint');

      if (mainsOn) {
        glow.style.opacity = '1';
        snow.style.opacity = '1';
        spark.style.opacity = '1';
        plug.setAttribute('transform', 'translate(110, 77)');
        cord.setAttribute('d', 'M 68 95 C 90 108 95 82 110 82');
        hint.textContent = 'Tap to unplug';
      } else {
        glow.style.opacity = '0';
        snow.style.opacity = '0';
        spark.style.opacity = '0';
        plug.setAttribute('transform', 'translate(95, 88)');
        cord.setAttribute('d', 'M 68 95 C 80 105 85 95 95 93');
        hint.textContent = 'Tap to plug in';
      }
    }
  </script>
</body>
</html>

Why can't we just run a refrigerator on a tiny AA battery, or carry a wall plug into the woods?

A **battery** is a self-contained power source that stores chemical energy and turns it into electrical energy whenever you turn a device on.

In 1800, scientist Alessandro Volta stacked discs of copper and zinc to create the very first battery, proving electricity could be stored in a portable container.

Batteries supply **low voltage**, which measures the push that moves electricity through a circuit. Most household batteries provide just 1.5 volts to 9 volts.

<!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;
      -webkit-tap-highlight-color: transparent;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #f8fafc;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 360px;
      padding: 12px;
      user-select: none;
    }

    /* Top Safety Badge */
    .badge {
      display: inline-flex;
      align-items: center;
      gap: 6px;
      background: #ecfdf5;
      color: #047857;
      border: 1.5px solid #a7f3d0;
      padding: 6px 14px;
      border-radius: 9999px;
      font-size: 14px;
      font-weight: 700;
      box-shadow: 0 1px 3px rgba(0,0,0,0.05);
    }

    .diagram-area {
      position: relative;
      width: 100%;
      max-width: 360px;
      height: 290px;
      margin-top: 4px;
    }

    /* SVG Overlay for connection rays */
    .lines-svg {
      position: absolute;
      inset: 0;
      width: 100%;
      height: 100%;
      pointer-events: none;
      z-index: 1;
    }

    .power-line {
      stroke: #cbd5e1;
      stroke-width: 2.5;
      stroke-dasharray: 5 4;
      transition: stroke 0.3s ease, stroke-width 0.3s ease;
    }

    .power-line.active {
      stroke: #22b7ff;
      stroke-width: 3.5;
      stroke-dasharray: 6 3;
      animation: dashFlow 0.8s linear infinite;
    }

    @keyframes dashFlow {
      to { stroke-dashoffset: -18; }
    }

    /* Center Battery */
    .center-battery {
      position: absolute;
      left: 50%;
      top: 50%;
      transform: translate(-50%, -50%);
      z-index: 3;
      display: flex;
      flex-direction: column;
      align-items: center;
      cursor: pointer;
    }

    .battery-shell {
      position: relative;
      width: 72px;
      height: 110px;
      background: linear-gradient(135deg, #1e293b 0%, #334155 100%);
      border-radius: 12px;
      border: 2px solid #0f172a;
      box-shadow: 0 0 18px rgba(34, 183, 255, 0.35);
      animation: pulseGlow 2.5s ease-in-out infinite alternate;
      display: flex;
      flex-direction: column;
      justify-content: space-between;
      overflow: hidden;
    }

    @keyframes pulseGlow {
      from { box-shadow: 0 0 10px rgba(34, 183, 255, 0.25); }
      to { box-shadow: 0 0 24px rgba(34, 183, 255, 0.65); }
    }

    .battery-terminal {
      width: 26px;
      height: 8px;
      background: #94a3b8;
      border-radius: 4px 4px 0 0;
      border: 2px solid #0f172a;
      border-bottom: none;
      margin-bottom: -1px;
    }

    .battery-gold-top {
      height: 30%;
      background: linear-gradient(180deg, #fbbf24, #d97706);
      display: flex;
      align-items: center;
      justify-content: center;
      font-weight: 900;
      color: #78350f;
      font-size: 14px;
    }

    .battery-body-label {
      flex: 1;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      color: #ffffff;
      text-align: center;
      gap: 2px;
    }

    .volt-text {
      font-size: 15px;
      font-weight: 800;
      color: #38bdf8;
      letter-spacing: 0.5px;
    }

    .sub-text {
      font-size: 11px;
      color: #94a3b8;
      font-weight: 600;
    }

    /* Device Nodes */
    .device-card {
      position: absolute;
      z-index: 2;
      width: 104px;
      padding: 8px 4px;
      background: #ffffff;
      border: 1.5px solid #e2e8f0;
      border-radius: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 4px;
      cursor: pointer;
      box-shadow: 0 2px 6px rgba(0,0,0,0.04);
      transition: border-color 0.25s ease, box-shadow 0.25s ease, background-color 0.25s ease;
    }

    .device-card:hover {
      box-shadow: 0 4px 12px rgba(34, 183, 255, 0.18);
    }

    .device-card.active {
      border-color: #22b7ff;
      background: #f0f9ff;
      box-shadow: 0 0 0 2px rgba(34, 183, 255, 0.3);
    }

    .device-icon {
      font-size: 24px;
      line-height: 1;
    }

    .device-title {
      font-size: 12px;
      font-weight: 700;
      color: #334155;
      text-align: center;
    }

    /* Quadrant Positioning */
    .pos-tl { top: 6px; left: 4px; }
    .pos-tr { top: 6px; right: 4px; }
    .pos-bl { bottom: 6px; left: 4px; }
    .pos-br { bottom: 6px; right: 4px; }
  </style>
</head>
<body>

  
  <div class="badge">
    <span>✓</span> Low Voltage = Safe &amp; Portable
  </div>

  
  <div class="diagram-area" id="diagramArea">
    <svg class="lines-svg" viewBox="0 0 360 290" preserveAspectRatio="none">
      
      <line id="line-0" class="power-line active" x1="140" y1="125" x2="80" y2="60" />
      
      <line id="line-1" class="power-line" x1="220" y1="125" x2="280" y2="60" />
      
      <line id="line-2" class="power-line" x1="140" y1="165" x2="80" y2="230" />
      
      <line id="line-3" class="power-line" x1="220" y1="165" x2="280" y2="230" />
    </svg>

    
    <div class="center-battery" id="batteryBtn" title="1.5V AA Battery">
      <div class="battery-terminal"></div>
      <div class="battery-shell">
        <div class="battery-gold-top">+</div>
        <div class="battery-body-label">
          <span class="volt-text">1.5 Volts</span>
          <span class="sub-text">AA Battery</span>
        </div>
      </div>
    </div>

    
    <div class="device-card pos-tl active" data-idx="0">
      <span class="device-icon">🎮</span>
      <span class="device-title">Game Console</span>
    </div>

    <div class="device-card pos-tr" data-idx="1">
      <span class="device-icon">📺</span>
      <span class="device-title">TV Remote</span>
    </div>

    <div class="device-card pos-bl" data-idx="2">
      <span class="device-icon">⌚</span>
      <span class="device-title">Digital Watch</span>
    </div>

    <div class="device-card pos-br" data-idx="3">
      <span class="device-icon">🚲</span>
      <span class="device-title">Bike Light</span>
    </div>
  </div>

  <script>
    const cards = document.querySelectorAll('.device-card');
    const lines = [
      document.getElementById('line-0'),
      document.getElementById('line-1'),
      document.getElementById('line-2'),
      document.getElementById('line-3')
    ];

    let currentIndex = 0;
    let autoPlayTimer = null;

    function activateDevice(index) {
      currentIndex = index;
      cards.forEach((c, i) => {
        if (i === index) {
          c.classList.add('active');
          lines[i].classList.add('active');
        } else {
          c.classList.remove('active');
          lines[i].classList.remove('active');
        }
      });
    }

    function startCycle() {
      if (autoPlayTimer) clearInterval(autoPlayTimer);
      autoPlayTimer = setInterval(() => {
        currentIndex = (currentIndex + 1) % cards.length;
        activateDevice(currentIndex);
      }, 3000);
    }

    cards.forEach((card, idx) => {
      card.addEventListener('click', () => {
        activateDevice(idx);
        startCycle(); // Reset timer after manual interaction
      });
    });

    document.getElementById('batteryBtn').addEventListener('click', () => {
      // Activate all simultaneously on center tap
      cards.forEach((c, i) => {
        c.classList.add('active');
        lines[i].classList.add('active');
      });
      if (autoPlayTimer) clearInterval(autoPlayTimer);
      setTimeout(startCycle, 2000);
    });

    startCycle();
  </script>
</body>
</html>

Because their voltage is low, batteries are safe to handle and make gadgets **portable**, meaning you can carry them anywhere.

What happens when an appliance needs hundreds of times more push than a small battery can give?

**Mains electricity** is high-power electricity made in large power stations and delivered directly into homes through wall sockets.

Wall sockets in the United States deliver **120 volts** of power—nearly 80 times stronger than a standard AA battery.

<!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;
      color: #1e2945;
      background: #ffffff;
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      min-height: 100%;
    }

    .flow-grid {
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 8px;
      position: relative;
    }

    @media (max-width: 520px) {
      .flow-grid {
        grid-template-columns: repeat(2, 1fr);
      }
    }

    .step-card {
      background: #f8fafc;
      border: 2px solid #e2e8f0;
      border-radius: 12px;
      padding: 10px 6px;
      text-align: center;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: space-between;
      min-height: 140px;
      cursor: pointer;
      transition: border-color 0.25s, box-shadow 0.25s, background-color 0.25s;
      user-select: none;
      position: relative;
    }

    .step-card.active {
      border-color: #22b7ff;
      background: #f0f9ff;
      box-shadow: 0 0 0 2px rgba(34, 183, 255, 0.25);
    }

    .step-num {
      font-size: 11px;
      font-weight: 700;
      color: #64748b;
      background: #e2e8f0;
      padding: 2px 8px;
      border-radius: 10px;
      margin-bottom: 4px;
    }

    .step-card.active .step-num {
      background: #22b7ff;
      color: #ffffff;
    }

    .icon-stage {
      height: 60px;
      display: flex;
      align-items: center;
      justify-content: center;
      position: relative;
      width: 100%;
    }

    .label {
      font-size: 13px;
      font-weight: 700;
      color: #1e2945;
      line-height: 1.2;
      margin-top: 4px;
    }

    /* Step 1: Generator */
    .gen-wheel {
      width: 42px;
      height: 42px;
      border-radius: 50%;
      border: 3px dashed #f59e0b;
      display: flex;
      align-items: center;
      justify-content: center;
      font-size: 20px;
      animation: spin 6s linear infinite;
    }

    @keyframes spin {
      from { transform: rotate(0deg); }
      to { transform: rotate(360deg); }
    }

    /* Step 2: Pylon */
    .pylon-icon {
      font-size: 32px;
      line-height: 1;
      filter: drop-shadow(0 2px 4px rgba(0,0,0,0.1));
    }
    .energy-spark {
      position: absolute;
      top: 8px;
      right: 14px;
      font-size: 14px;
      animation: pulse 1.5s ease-in-out infinite;
    }

    @keyframes pulse {
      0%, 100% { opacity: 0.3; transform: scale(0.9); }
      50% { opacity: 1; transform: scale(1.2); }
    }

    /* Step 3: Outlet */
    .outlet-box {
      width: 40px;
      height: 48px;
      background: #ffffff;
      border: 2px solid #94a3b8;
      border-radius: 6px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      gap: 5px;
      box-shadow: inset 0 1px 3px rgba(0,0,0,0.1);
    }
    .socket-holes {
      display: flex;
      gap: 6px;
    }
    .socket-hole {
      width: 4px;
      height: 10px;
      background: #334155;
      border-radius: 2px;
    }
    .ground-hole {
      width: 6px;
      height: 6px;
      background: #334155;
      border-radius: 50%;
    }

    /* Step 4: Appliances */
    .appliance-row {
      display: flex;
      gap: 4px;
      font-size: 22px;
      align-items: center;
      justify-content: center;
    }

    /* Controls */
    .controls {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      padding: 2px 0;
    }

    .btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      border-radius: 6px;
      padding: 6px 12px;
      font-size: 13px;
      font-weight: 600;
      color: #334155;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 4px;
    }
    .btn:active {
      background: #e2e8f0;
    }

    .dots {
      display: flex;
      gap: 6px;
    }
    .dot {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: #cbd5e1;
      cursor: pointer;
      transition: background-color 0.2s, transform 0.2s;
    }
    .dot.active {
      background: #22b7ff;
      transform: scale(1.25);
    }

    /* Warning Badge */
    .warning-badge {
      background: #fef9c3;
      border: 1.5px solid #facc15;
      border-radius: 8px;
      padding: 8px 12px;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      color: #854d0e;
      font-size: 12px;
      font-weight: 700;
      text-align: center;
      line-height: 1.3;
    }
    .warning-badge span {
      font-size: 16px;
    }
  </style>
</head>
<body>

  <div class="flow-grid" id="flowGrid">
    
    <div class="step-card active" data-step="0">
      <span class="step-num">Step 1</span>
      <div class="icon-stage">
        <div class="gen-wheel">⚙️</div>
      </div>
      <div class="label">Power<br>Station</div>
    </div>

    
    <div class="step-card" data-step="1">
      <span class="step-num">Step 2</span>
      <div class="icon-stage">
        <span class="pylon-icon">🗼</span>
        <span class="energy-spark">⚡</span>
      </div>
      <div class="label">Power<br>Lines</div>
    </div>

    
    <div class="step-card" data-step="2">
      <span class="step-num">Step 3</span>
      <div class="icon-stage">
        <div class="outlet-box">
          <div class="ground-hole"></div>
          <div class="socket-holes">
            <div class="socket-hole"></div>
            <div class="socket-hole"></div>
          </div>
        </div>
      </div>
      <div class="label">Wall<br>Outlet</div>
    </div>

    
    <div class="step-card" data-step="3">
      <span class="step-num">Step 4</span>
      <div class="icon-stage">
        <div class="appliance-row">
          <span title="Microwave">📻</span>
          <span title="Washing Machine">🫧</span>
          <span title="Stove">🍳</span>
        </div>
      </div>
      <div class="label">Mains<br>Appliances</div>
    </div>
  </div>

  <div class="controls">
    <button class="btn" id="playBtn">⏸ Pause</button>
    <div class="dots">
      <div class="dot active" data-step="0"></div>
      <div class="dot" data-step="1"></div>
      <div class="dot" data-step="2"></div>
      <div class="dot" data-step="3"></div>
    </div>
  </div>

  <div class="warning-badge">
    <span>⚠️</span>
    <div>High Voltage: Never touch socket pins or damaged cords!</div>
  </div>

  <script>
    const cards = document.querySelectorAll('.step-card');
    const dots = document.querySelectorAll('.dot');
    const playBtn = document.getElementById('playBtn');
    let currentStep = 0;
    let isPlaying = true;
    let timer = null;

    function setStep(index) {
      currentStep = index;
      cards.forEach((card, i) => {
        card.classList.toggle('active', i === currentStep);
      });
      dots.forEach((dot, i) => {
        dot.classList.toggle('active', i === currentStep);
      });
    }

    function nextStep() {
      setStep((currentStep + 1) % cards.length);
    }

    function startTimer() {
      stopTimer();
      timer = setInterval(nextStep, 3000);
    }

    function stopTimer() {
      if (timer) clearInterval(timer);
    }

    cards.forEach((card, i) => {
      card.addEventListener('click', () => {
        setStep(i);
        if (isPlaying) startTimer();
      });
    });

    dots.forEach((dot, i) => {
      dot.addEventListener('click', () => {
        setStep(i);
        if (isPlaying) startTimer();
      });
    });

    playBtn.addEventListener('click', () => {
      isPlaying = !isPlaying;
      if (isPlaying) {
        playBtn.textContent = '⏸ Pause';
        startTimer();
      } else {
        playBtn.textContent = '▶ Play';
        stopTimer();
      }
    });

    startTimer();
  </script>
</body>
</html>

Appliances that create lots of heat or run giant motors—like toasters, air conditioners, and ovens—need this powerful mains supply.

Because mains electricity has such high voltage, it can cause severe electric shocks, which is why wall outlets require strict safety rules.

How can you instantly tell which power source an appliance uses?

When deciding how to power a machine, engineers look at two things: how much energy it needs and whether it must move around.

<!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;
      -webkit-tap-highlight-color: transparent;
    }

    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      background: #ffffff;
      color: #1e2945;
      padding: 10px;
      display: flex;
      flex-direction: column;
      justify-content: center;
      min-height: 100%;
    }

    .grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
      width: 100%;
      max-width: 620px;
      margin: 0 auto;
    }

    .column {
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

    /* Column Headers */
    .col-header {
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 8px 10px;
      border-radius: 8px;
      font-weight: 700;
      font-size: 14px;
    }

    .battery-header {
      background: #ecfdf5;
      color: #065f46;
      border: 1px solid #a7f3d0;
    }

    .mains-header {
      background: #eff6ff;
      color: #1e40af;
      border: 1px solid #bfdbfe;
    }

    .badge {
      font-size: 11px;
      font-weight: 600;
      padding: 2px 6px;
      border-radius: 12px;
      text-transform: uppercase;
      letter-spacing: 0.3px;
    }

    .battery-badge {
      background: #10b981;
      color: #ffffff;
    }

    .mains-badge {
      background: #3b82f6;
      color: #ffffff;
    }

    /* Device Cards */
    .device-card {
      display: flex;
      align-items: center;
      gap: 10px;
      padding: 8px 10px;
      background: #ffffff;
      border: 1px solid #e5e7eb;
      border-radius: 8px;
      cursor: pointer;
      transition: background-color 0.2s ease, border-color 0.2s ease, box-shadow 0.2s ease;
    }

    .device-card:hover, .device-card.active {
      box-shadow: 0 2px 6px rgba(0, 0, 0, 0.06);
    }

    .battery-card:hover, .battery-card.active {
      border-color: #10b981;
      background: #f0fdf4;
    }

    .mains-card:hover, .mains-card.active {
      border-color: #3b82f6;
      background: #f0f9ff;
    }

    .device-icon {
      font-size: 24px;
      line-height: 1;
      flex-shrink: 0;
    }

    .device-info {
      display: flex;
      flex-direction: column;
      min-width: 0;
    }

    .device-name {
      font-size: 13px;
      font-weight: 600;
      color: #1e2945;
      white-space: nowrap;
      overflow: hidden;
      text-overflow: ellipsis;
    }

    .device-tag {
      font-size: 11px;
      color: #6b7280;
      margin-top: 1px;
    }

    .power-level {
      margin-left: auto;
      font-size: 10px;
      font-weight: 700;
      letter-spacing: -1px;
      padding-left: 4px;
      flex-shrink: 0;
    }

    .battery-level {
      color: #059669;
    }

    .mains-level {
      color: #2563eb;
    }

    @media (max-width: 380px) {
      body {
        padding: 6px;
      }
      .grid {
        gap: 8px;
      }
      .col-header {
        padding: 6px 8px;
        font-size: 13px;
      }
      .badge {
        font-size: 10px;
        padding: 1px 4px;
      }
      .device-card {
        padding: 6px 8px;
        gap: 8px;
      }
      .device-icon {
        font-size: 20px;
      }
      .device-name {
        font-size: 12px;
      }
      .device-tag {
        font-size: 10px;
      }
    }
  </style>
</head>
<body>

  <div class="grid">
    
    <div class="column">
      <div class="col-header battery-header">
        <span>🔋 Battery</span>
        <span class="badge battery-badge">Portable</span>
      </div>

      <div class="device-card battery-card" onclick="highlight(this)">
        <span class="device-icon">🔦</span>
        <div class="device-info">
          <span class="device-name">Flashlight</span>
          <span class="device-tag">Carried outside</span>
        </div>
        <span class="power-level battery-level">⚡</span>
      </div>

      <div class="device-card battery-card" onclick="highlight(this)">
        <span class="device-icon">📺</span>
        <div class="device-info">
          <span class="device-name">TV Remote</span>
          <span class="device-tag">Moves around</span>
        </div>
        <span class="power-level battery-level">⚡</span>
      </div>

      <div class="device-card battery-card" onclick="highlight(this)">
        <span class="device-icon">🖱️</span>
        <div class="device-info">
          <span class="device-name">Mouse</span>
          <span class="device-tag">Cordless desk</span>
        </div>
        <span class="power-level battery-level">⚡</span>
      </div>
    </div>

    
    <div class="column">
      <div class="col-header mains-header">
        <span>🔌 Mains</span>
        <span class="badge mains-badge">Wall Plug</span>
      </div>

      <div class="device-card mains-card" onclick="highlight(this)">
        <span class="device-icon">🍞</span>
        <div class="device-info">
          <span class="device-name">Toaster</span>
          <span class="device-tag">Huge heat</span>
        </div>
        <span class="power-level mains-level">⚡⚡⚡</span>
      </div>

      <div class="device-card mains-card" onclick="highlight(this)">
        <span class="device-icon">🧺</span>
        <div class="device-info">
          <span class="device-name">Washer</span>
          <span class="device-tag">Heavy motor</span>
        </div>
        <span class="power-level mains-level">⚡⚡⚡</span>
      </div>

      <div class="device-card mains-card" onclick="highlight(this)">
        <span class="device-icon">🍲</span>
        <div class="device-info">
          <span class="device-name">Microwave</span>
          <span class="device-tag">Fast cooking</span>
        </div>
        <span class="power-level mains-level">⚡⚡⚡</span>
      </div>
    </div>
  </div>

  <script>
    function highlight(el) {
      document.querySelectorAll('.device-card').forEach(c => c.classList.remove('active'));
      el.classList.add('active');
    }
  </script>
</body>
</html>

A common mistake is thinking rechargeable devices like smartphones run on mains power because you plug them into a wall.

Your phone actually runs on an internal **rechargeable battery**; the wall charger simply refills the battery's stored chemical energy so you can unplug and walk away.

Next time you use a gadget, check: does it stay plugged in for high power, or does it pack its own portable battery?

science

What Is Electricity? Mains vs Battery Power. Distinguish between battery-powered appliances and high-voltage mains electricity.

Electrical Appliances (KS2 / Year 4 Science - Unit: Electrical Circuits)

What is Electricity? - KS2 Science

Primary Science: Electricity and Appliances in the Home and School

Pedagogical strategy focuses on concrete-to-abstract progression: begin with a classroom scavenger hunt identifying appliances, transition to a physical or digital 3-way sorting activity (Mains / Battery / Both), reinforce safety principles through contrasting voltage values ($230\text{ V}$ vs. $1.5\text{ V}$), and conclude with hands-on low-voltage cell exploration to prepare students for constructing simple series circuits.

What Is Electricity? Mains vs Battery Power

Battery Power

Mains Electricity