Question

Three identical bulbs are connected as shown in figure. When switch S is closed, the power consumed in bulb Bis P. What will be the power consumed by the same bulb when switch S is opened?

1) 9P/4
2) 16P/9
3) 9P/16
4) 4P/9


Answer is Option 1. Give detailed explanation.

Answer 1

4) 4P/9

Explanation:

Given that all bulbs are identical So voltage across bulbs = E / 2 by voltage divider rule.

So, R = V^2 / P = E^2 / 4P

When S is closed, effective resistance of B and C = R * R / (R+R) = R/ 2

Voltage across B = (R/2) / (3R/2) * E = E / 3

Power consumed by B = (E/3)^2 / R = E^2 * 4P / 9 * E^2 = 4P / 9

Option 4 is the correct answer.

Answer 2

Answer: we get the power consumed by the same bulb when switch S is opened as 4P/9

Hence, option D is the correct answer.