EASA / CAR Part-66 · Module 3 · 3.6 DC Circuits · Cat A · B1/B2

Ohm's Law, V = I × R

Objective: in a resistor the current is proportional to the voltage and inversely proportional to the resistance, V = I·R. Set the supply and the resistance and watch the current, the power dissipated, and the electrons flow faster or slower.

Circuit, with electron flow & meters

Current vs voltage

Supply voltage V 12 V

Resistance R 40 Ω

Voltage V

Current I

Resistance R

0Ω

Power P = V·I

V = I·R → I = V/R · Power: P = V·I = I²·R = V²/R

Voltage is the electrical "push" that drives current through a circuit; resistance opposes it. Ohm's law ties the three together: the current equals the voltage divided by the resistance, I = V/R. Double the voltage and the current doubles; double the resistance and the current halves. The current–voltage graph of a fixed resistor is a straight line through the origin, and its slope is 1/R, a steeper line means a smaller resistance. The power turned into heat in the resistor is P = V·I, which you can also write as I²R or V²/R.

Try this: Raise the voltage and watch the current, and the electron speed, rise in proportion.
Try this: Increase the resistance at fixed voltage; the current falls and the graph line becomes less steep.
Try this: Find a V and R that give exactly 1 A, then check P = V × I.
Try this: Set R small and V high, watch the power (and heat) climb quickly, since P = V²/R.