What Ohm’s law says
Ohm’s law is the workhorse equation of every electric circuit. It ties three quantities together:
V = I × R
- V is the voltage (in volts, V) — the “push” that drives charge.
- I is the current (in amperes, A) — how much charge flows per second.
- R is the resistance (in ohms, Ω) — how much the material opposes the flow.
Because the three are linked, knowing any two pins down the third. Rearranging the same equation gives I = V ÷ R and R = V ÷ I. Use the “Solve for” buttons in the widget to pick which one you want the circuit to compute, then drag the two sliders and watch the answer update instantly.
Power and the glowing bulb
Voltage and current together set the electrical power a component uses:
P = V × I (in watts, W)
Power is the rate at which electrical energy is converted into other forms — heat and light in a bulb, motion in a motor. In the interactive, the light bulb’s glow brightens as the power rises, so you can see the difference between a dim, low-power circuit and a bright, high-power one. Try holding the resistance steady and raising the voltage: current climbs, and the bulb gets noticeably brighter because power grows with the square of the voltage when resistance is fixed.
A worked example
With V = 6 V and R = 10 Ω, current is I = 6 ÷ 10 = 0.6 A, and the power is P = 6 × 0.6 = 3.6 W. Double the voltage to 12 V (same resistance) and the current doubles to 1.2 A while the power quadruples to 14.4 W — a great way to show students why high-power devices draw so much.
Using this with a class
Project the widget and call out a target — “make the bulb as bright as you can with the resistance fixed at 20 Ω” — or give two values and have students predict the third before they release the slider. It’s free to embed on a class site or LMS page.