Question

Three equal resistors connected in series across a source of emf together dissipate $10W$ of power. What should be the power dissipated if the same resistors are connected in parallel across the same source of emf?

• A. $9W$
• B. $90W$
• C. $10W$
• D. $100W$

Answer 1

The correct option is B $90W$

Case 1:- (When connected in series)

$R_{net}=R+R+R=3R$

Power dissipated$=\cfrac{V^{2}}{R_{net}}=\cfrac{V^{2}}{3R}=10W

$\frac{V^2}{R}=30W$

Case 2:-(When connected in parallel)

$R_{net}=\frac{R}{3}$

Power dissipated$=\frac{V^2}{R_{net\left(Case2\right)}}=3\left(\frac{V^2}{R}\right)$

$=3\times 30W=90W$

Figure1 represents Case 1.

Figure 2 represents Case 2.