QuizOhm's law · 6 min
Quiz: Ohm's law
7 questions. Answer each one, then open Show the answer to check yourself. In Litmux Academy the quiz is marked and counts towards your certificate.
Question 1What current flows through 2 kΩ with 10 V across it?
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Answer: 5 mA
I = V / R = 10 / 2 kΩ = 5 mA.
Question 2A resistor has 3 V across it and 1.5 mA through it. Its resistance is:
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Answer: 2000 Ω
R = V / I = 3 / 0.0015 = 2000 Ω.
Question 3The voltage across a resistor is doubled. Its current:
- halves
- stays the same
- doubles
- quadruples
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Answer: C. doubles
I = V / R: proportional to V.
Question 4Which resistor runs a red LED (2 V) at 20 mA from 5 V?
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Answer: 150 Ω
R = (5 − 2) / 0.02 = 150 Ω.
Question 5To measure the current through a resistor, the multimeter goes:
- across the resistor, on V⎓
- in series with it, red lead in the A socket, on A⎓
- across the battery, on A⎓
- anywhere, on Ω
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Answer: B. in series with it, red lead in the A socket, on A⎓
Current must pass through the meter: break the loop and put the meter in the gap.
Question 6Why does an LED not follow Ohm's law the way a resistor does?
- It has no resistance
- Its current rises steeply once its voltage passes about 2 V, so R = V / I is not constant
- It only works on AC
- It is an insulator
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Answer: B. Its current rises steeply once its voltage passes about 2 V, so R = V / I is not constant
An LED's I-V curve is exponential, not a straight line.
Question 7A 0.05 Ω shunt shows 0.1 V. What is the current?
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Answer: 2 A
I = 0.1 / 0.05 = 2 A.