Answer key: Ohm’s Law & Electrical Power Worksheet
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Goal: Find how voltage and resistance set the current in a circuit (V = IR), and how much power the resistor uses (P = VI).
Completed results table
| Setting | Current | Power |
|---|---|---|
| Default (12 V, 100 Ω) | 0.12 A | 1.44 W |
| Low resistance (12 V, 20 Ω) | 0.6 A | 7.2 W |
| Higher voltage (24 V, 100 Ω) | 0.24 A | 5.76 W |
| No voltage (0 V, 100 Ω) | 0 A | 0 W |
| 12 V, 200 Ω | 0.06 A | 0.72 W |
| 24 V, 200 Ω | 0.12 A | 2.88 W |
Answers
What happened to the current when you doubled the voltage from 12 V to 24 V? Use V = IR to explain.
It doubled, from 0.12 A to 0.24 A. With the resistance fixed, I = V ÷ R, so the current is proportional to the voltage.
What happened to the current when you doubled the resistance from 100 Ω to 200 Ω?
It halved, from 0.12 A to 0.06 A: with the voltage fixed, doubling R halves I = V ÷ R.
Doubling the voltage multiplied the power by 4. Explain why, using P = VI.
Both V and I doubled, so P = VI went up 2 × 2 = 4 times, from 1.44 W to 5.76 W. The same result follows from P = V² ÷ R.
The 24 V, 200 Ω circuit carries the same current as the default circuit. Does it use the same power?
No. Both carry 0.12 A, but the power is 2.88 W instead of 1.44 W, because P = I²R and the resistance is twice as large.
“Low resistance” draws 0.6 A and uses 7.2 W. Why can a very low resistance be dangerous in real wiring?
Current grows as resistance falls (I = 12 ÷ 20 = 0.6 A), and so does the power turned into heat, here 7.2 W. A short circuit has almost no resistance, so a huge current heats the wires; fuses and circuit breakers cut it off.
Challenge: what resistance would let exactly 0.5 A flow from the 12 V supply? Calculate it, then type it into the lab to check.
R = V ÷ I = 12 ÷ 0.5 = 24 Ω, and the lab shows a current of 0.5 A at 24 Ω.