question_answer

  In the following circuit, bulb rated as 1.5 V, 0.45 W. If bulbs glows with full intensity then what will be the equivalent resistance between X and Y

A)            0.45 W

B)            1 W

C)            3 W

D)            5 W

Correct Answer: B

Solution :

                   When bulb glows with full intensity, then voltage across it will be 1.5 V and voltage across 3 W resistance will be 4.5 V. Current through 3 W resistance \[i=\frac{4.5}{3}=1.5A\] Same current will flow between X and Y So \[{{V}_{XY}}=i{{R}_{XY}}\] Þ \[1.5=1.5{{R}_{XY}}\] Þ \[{{R}_{XY}}=1\Omega \]