lesson
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You connect a mystery resistor to a power supply, crank the voltage, and plot the readings. How can the angle of a single straight line immediately tell you the exact resistance of the component?
In 1827, German physicist Georg Ohm discovered that for a metal wire kept at a constant temperature, the current flowing through it is directly proportional to the potential difference across it.
This relationship is Ohm's Law, written as V=IรR, where V is potential difference in volts (V), I is current in amperes (A), and R is resistance in ohms (ฮฉ).
๐Create a clean visual card showing Ohm's Law and an Ohmic conductor graph. At top: Ohm's law formula triangle with V on top, I and R below, plus the rearranged form R = V / I. Below: A clean 2D coordinate grid showing a straight line through the origin (0,0) labeled 'Ohmic Conductor (Constant Temperature)'. Use a crisp modern palette (#1e2945 text, #2563eb blue line, #f8f9fa background card, subtle grid lines). Responsive layout for 350px width.
Physics exams often swap which variable sits on the vertical axis, completely changing how you calculate resistance. How do you handle a graph when voltage is on the vertical axis?
Reading V-I Graphs Directly
On a V-I graph, voltage V is plotted on the vertical y-axis and current I is plotted on the horizontal x-axis.
The gradient (or slope) of a straight line is the change in the vertical value divided by the change in the horizontal value: gradient=ฮxฮyโ.
๐A diagram of a V-I graph with Voltage (V) on the vertical y-axis and Current (A) on the horizontal x-axis. A straight line passes through (0,0) to a point (0.5, 6.0). A dashed right-angle triangle highlights delta V = 6.0 V (vertical leg in green) and delta I = 0.5 A (horizontal leg in blue). A callout bubble shows: Gradient = delta V / delta I = 6.0 / 0.5 = 12 Omega. Clean modern style with bold labels and contrasting colors (#1e2945, #10b981, #2563eb).
Because gradient=ฮIฮVโ and Ohm's Law states R=IVโ, the gradient of a V-I graph gives resistance directly: R=gradient.
For the line shown in the diagram, the resistance calculation is simply R=0.5ย Aโ0ย A6.0ย Vโ0ย Vโ=12ย ฮฉ.
What happens when current is placed on the vertical axis instead?