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CBET Electronics Quiz

Ohm's Law Quiz

Practice calculating voltage, current, and resistance in DC resistive circuits, from basic substitution to series loads and signal-sensing resistors.

These 25 questions focus on calculations, mA and kΩ conversions, voltage drops, and power. Submit all answers to see your score and a worked solution for every question.

Start the 25-Question Quiz Review Ohm's Law First Voltage Current Resistance
25Practice questions
V = I × RCore formula
CBETElectronics foundation

Before You Start

Ohm's Law connects voltage, current, and resistance. This quiz uses ideal DC sources and resistive loads unless otherwise stated. It is calculation practice; the voltage, current, and resistance quiz provides the beginner concept review.

V = I × R

Unit reminders: 1 A = 1,000 mA; 1 mA = 1,000 µA; 1 kΩ = 1,000 Ω. For resistor power, use P = V × I.

Simple pattern: Voltage pushes, resistance limits, and current changes.
Common mistake: Do not memorize the formula only. Pay attention to what changes first in the question.

Choose one answer for each question. A calculator is welcome. Convert mA to A and kΩ to Ω before substituting values; round only when a question requests it.

If a calculation question gives voltage and resistance, use I = V ÷ R. If it gives voltage and current, use R = V ÷ I. If it gives current and resistance, use V = I × R.

1. A 12 V DC source supplies a 150 Ω resistor. What current flows?
2. A 24 V source supplies a 1.2 kΩ resistor. What current flows?
3. A resistor carries 15 mA and measures 680 Ω. What voltage is across it?
4. A resistive load draws 30 mA from a 9 V source. What is its resistance?
5. A 5 V source is connected across a 2.5 kΩ resistor. What current flows?
6. A resistor carries 0.4 A with a 6 V drop across it. What is its resistance?
7. A 47 Ω resistor carries 200 mA. What voltage is across it?
8. A 250 Ω resistor carries 12 mA. What voltage is across it?
9. A 3.3 V source supplies a 330 Ω resistor. What current flows?
10. A resistor has 0.5 V across it and carries 250 µA. What is its resistance?
11. A 12 V ideal source supplies two series resistors: 100 Ω and 200 Ω. What current flows through both?
12. A 10 V ideal source supplies a series pair of 100 Ω and 400 Ω. What is the voltage across the 400 Ω resistor?
13. A 24 V ideal source supplies two parallel branches of 1.2 kΩ each. What total current leaves the source?
14. A 12 V ideal source supplies parallel resistors of 600 Ω and 300 Ω. What is the current through the 300 Ω branch?
15. A resistor carries 20 mA at 12 V. If its resistance stays fixed and voltage falls to 9 V, what current flows?
16. A resistive circuit draws 50 mA. Its source voltage is doubled and its resistance is tripled. What is the new current, rounded to one decimal place?
17. A resistive test load normally draws 100 mA at 12 V. It now draws 80 mA with the same 12 V across it. What is its effective resistance now?
18. A 100 Ω resistive load now draws 90 mA instead of the expected 120 mA. What voltage is presently across the load?
19. An ideal 10 V source supplies a 100 Ω load in series with a connector that adds 25 Ω. What voltage is across the load?
20. A 4–20 mA signal flows through a 250 Ω sensing resistor. What voltage corresponds to 16 mA?
21. A 250 Ω sensing resistor has 3 V across it. What signal current flows?
22. A 12 V resistive branch must draw 8 mA. What resistance is required?
23. A 24 V source supplies a 600 Ω resistor. What power does the resistor dissipate?
24. A resistor has 10 V across it and carries 50 mA. What power does it dissipate?
25. An ideal 12 V source supplies two series resistors. One is 100 Ω, and measured current is 30 mA. What is the other resistance?

Your Result

Worked Answers

Compare your calculation with the formula, unit conversion, and result for each question.

Question 1 — 0.08 A: I = V ÷ R = 12 ÷ 150 = 0.08 A, or 80 mA.
Question 2 — 20 mA: Convert 1.2 kΩ to 1,200 Ω. I = 24 ÷ 1,200 = 0.02 A = 20 mA.
Question 3 — 10.2 V: Convert 15 mA to 0.015 A. V = I × R = 0.015 × 680 = 10.2 V.
Question 4 — 300 Ω: I = 0.030 A. R = V ÷ I = 9 ÷ 0.030 = 300 Ω.
Question 5 — 2 mA: R = 2,500 Ω. I = 5 ÷ 2,500 = 0.002 A = 2 mA.
Question 6 — 15 Ω: R = V ÷ I = 6 ÷ 0.4 = 15 Ω.
Question 7 — 9.4 V: 200 mA = 0.2 A. V = 0.2 × 47 = 9.4 V.
Question 8 — 3 V: 12 mA = 0.012 A. V = 0.012 × 250 = 3 V.
Question 9 — 10 mA: I = 3.3 ÷ 330 = 0.01 A = 10 mA.
Question 10 — 2 kΩ: 250 µA = 0.000250 A. R = 0.5 ÷ 0.000250 = 2,000 Ω = 2 kΩ.
Question 11 — 40 mA: Series resistance is 100 + 200 = 300 Ω. I = 12 ÷ 300 = 0.04 A = 40 mA. Both series resistors carry the same current.
Question 12 — 8 V: Total resistance is 500 Ω. I = 10 ÷ 500 = 0.02 A. The 400 Ω drop is 0.02 × 400 = 8 V; the other resistor drops 2 V.
Question 13 — 40 mA: Each branch carries 24 ÷ 1,200 = 20 mA. Total current is 20 + 20 = 40 mA.
Question 14 — 40 mA: Each parallel branch has the full 12 V across it. For the 300 Ω branch, I = 12 ÷ 300 = 40 mA. The total source current would be 60 mA.
Question 15 — 15 mA: R = 12 ÷ 0.020 = 600 Ω. At 9 V, I = 9 ÷ 600 = 0.015 A = 15 mA.
Question 16 — 33.3 mA: I scales as V ÷ R. New current = 50 × 2 ÷ 3 = 33.333… mA, which rounds to 33.3 mA.
Question 17 — 150 Ω: Use the present measurements: R = 12 ÷ 0.080 = 150 Ω. Its normal resistance was 120 Ω.
Question 18 — 9 V: Use the measured current: V = 0.090 × 100 = 9 V. At 120 mA the same resistance would have 12 V across it.
Question 19 — 8 V: Total resistance is 125 Ω, so I = 10 ÷ 125 = 0.08 A. The load voltage is 0.08 × 100 = 8 V. The connector drops 2 V.
Question 20 — 4 V: V = I × R = 0.016 × 250 = 4 V. For comparison, 4 mA produces 1 V and 20 mA produces 5 V.
Question 21 — 12 mA: I = 3 ÷ 250 = 0.012 A = 12 mA.
Question 22 — 1.5 kΩ: 8 mA = 0.008 A. R = 12 ÷ 0.008 = 1,500 Ω = 1.5 kΩ.
Question 23 — 0.96 W: I = 24 ÷ 600 = 0.04 A. P = V × I = 24 × 0.04 = 0.96 W. Equivalently, P = V² ÷ R.
Question 24 — 0.5 W: 50 mA = 0.05 A. P = V × I = 10 × 0.05 = 0.5 W.
Question 25 — 300 Ω: Total resistance is R = 12 ÷ 0.030 = 400 Ω. Subtract the known 100 Ω: the other resistor is 300 Ω.
Review Ohm's Law Review Voltage vs Current vs Resistance Try Voltage Current Resistance Quiz CBET Electronics Practice Browse All Practice Tools

Best Study Path After This Quiz

This quiz pairs directly with the Ohm's Law guide. After this, keep moving through the electronics foundation path.

1. What Is Ohm's Law? Review the formula, examples, and behavior rules. 2. Voltage Current Resistance Review the foundation behind the formula. 3. Power Supply Basics See how this applies in real equipment. 4. CBET Electronics Practice Practice mixed electronics concepts.

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Ready for mixed electronics practice?

After Ohm's Law, move into broader CBET electronics questions covering power supplies, AC/DC, components, and troubleshooting.

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For learning purposes only. These are simplified circuit calculations, not equipment service instructions. Follow manufacturer procedures and appropriate electrical safety practices. Resistance measurements require an isolated, de-energized circuit with stored energy safely discharged.