A heating element with a resistance of 24 Ω is connected to a 120 V source. How much current does it draw?
Answer in A.
Show the answer
5 A
I = E ÷ R = 120 V ÷ 24 Ω = 5 A.
Reference: Ohm's law, I = E ÷ R
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Ohm's law power practice questions
35 questions from the electrical theory and calculations practice test.
Ohm's law power practice test
10 questions, graded as you go, with the reason for every answer. No sign-up.
What this covers
- Units
- Ohm's law
- Power
- Power at other than rated voltage
- Energy
- Energy cost
- Efficiency
- Power with line resistance
Sample questions
A current of 8 A flows through a 15 Ω resistor. What is the voltage across the resistor?
Answer in V.
Show the answer
120 V
E = I × R = 8 A × 15 Ω = 120 V.
Reference: Ohm's law, E = I × R
A load connected to a 240 V circuit draws 12 A. What is the resistance of the load?
- 2,880 Ω
- 20 Ω
- 0.05 Ω
- 228 Ω
Show the answer
B. 20 Ω
R = E ÷ I = 240 ÷ 12 = 20 Ω. Multiplying 240 × 12 = 2,880 gives the power in watts, not the resistance, and 0.05 is the formula inverted.
Reference: Ohm's law, R = E ÷ I