Question

Three equal resistors connected in series across a source of e.m.f. together dissipate 10 watt of power. What will be the power dissipated in watt if the same resistors are connected in parallel across the same source of e.m.f. ?

• A. 30
• B. $\frac{10}{3}$
• C. 10
• D. 90

Answer 1

Answer: (D)

90

Answer 2

For series, $R_{eq}=3r$
Power $=\frac{V^2}{3r}= 10 \Rightarrow \frac{V^2}{r}=30.$
For parallel $R_{eq}=r/3$
Power $=\frac{V^2}{r/3}= \frac{3V^2}{r} = 3 \times 30 = 90\, watt.$