Question

Two lamps have resistance $r$ and $R(R>r)$. If they are connected in parallel in an electric circuit, then :

• A. The lamp with resistance $R$ will shine more brightly.
• B. The lamp with resistance $r$ will shine more brightly.
• C. The two lamps will shine equally brightly.
• D. The lamp with resistance $R$ will not shine at all.

Answer 1

Answer: (B)

The lamp with resistance $r$ will shine more brightly.

Power $=\frac{V^2}{R}$

When connected in parallel both the bulbs have same $V$

$\Rightarrow P_1=\frac{V^2}{r}:P_2=\frac{V^2}{R}$

$r=\frac{V^2}{P_1}:R=\frac{V^2}{P_2}$

Given $R>r$

$\Rightarrow \frac{1}{P_2}>\frac{1}{P_1}$

$\Rightarrow P_1>P_2$

$\therefore$ Bulb with resistance $r$ shines more brightly.