In the circuit shown, which resistor turns more electrical energy into heat each second, and at what rate? A 12 V battery connected across two resistors in parallel, R1 = 4 Ω and R2 = 12 Ω, each on its own branch.

In the circuit shown, which resistor turns more…

In the circuit shown, which resistor turns more electrical energy into heat each second, and at what rate?

Question 58

HardOriginal question

In the circuit shown, which resistor turns more electrical energy into heat each second, and at what rate?

A 12 V battery connected across two resistors in parallel, R1 = 4 Ω and R2 = 12 Ω, each on its own branch.

R2, at 12 WCorrect answerYour answerR1, at 36 WCorrect answerYour answerR2, at 36 WCorrect answerYour answerBoth equally, at 24 W eachCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer B

Correct answer: B

In parallel both resistors have the full 12 V across them.
P = V² ÷ R: R1 gives 144 ÷ 4 = 36 W and R2 gives 144 ÷ 12 = 12 W.
So the smaller resistor, R1, uses more power.

Worth noting

In series the larger resistor uses more power (P = I²R, same I); in parallel the smaller one does (P = V²/R, same V).

Concept: Power in parallel resistors
Typical timeTypical: 90 s
Your timeYours: —

The rule this testsElectricity and magnetism

Practise this chapter →

Ten questions from Everyday Physics, at your own pace.

Practise this chapter →

Ten questions from Everyday Physics, at your own pace.

In the circuit shown, which resistor turns more electrical energy into heat each second, and at what rate?

Question 58

Explanation