Two heaters A and B have power rating of 1 kW and 2 kW, respectively. Those two are first connected in series and then in parallel to a fixed power source. The ratio of power outputs for these two cases is:

1. 2 : 3

2. 1 : 1

3. 2 : 9

4. 1 : 2

Doubtly Asked 30 Oct 2026 NEET UG 2024 Practice test neet Save WhatsApp Report

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Answer: 3. 2 : 9

Key idea: \(P=\frac{V^2}{R}\), so \(R\propto\frac1P\) at fixed voltage.

Take \(R_A=2\) units (1 kW) and \(R_B=1\) unit (2 kW).

Series: \(R_s=3\), so \(P_s=\frac{V^2}{3}\).
Parallel: \(R_p=\frac{2\times1}{3}=\frac23\), so \(P_p=\frac{3V^2}{2}\). (Also \(P_p=1+2=3\) kW directly.)

\(\frac{P_s}{P_p}=\frac{1/3}{3/2}=\frac29\). So the ratio is 2 : 9, option 3.

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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