Question

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

(1)  0.45 Ω

 (2)  1 Ω

(3)  3 Ω

(4)  5 Ω

Answer 1

Correct option  (2)  1 Ω

Explanation:

P = 0.45 W, V = 1.5 V

When bulb glows with full intensity, voltage across it must be 1.5v. 

(I) current through 3Ω =  4.5/3 = 1.5A

V_x - V_y = I(R_xy) = 1.5(R_xy)

R_xy = 1 Ω