An electric bulb of 60 ~W , 120 ~V is to be connected to 220 V source. What resistance should be connected in series with the bulb, so that the bulb glows properly?

Step-by-step solution

Resistance of the bulb, R= V^2 P = 120 120 60 =240 il I= P V = 60 120 =0.5 ~A Since, bulb is connected with 220 V supply. Resistance required, R^ = V I = 220 0.5 =440 Thus, for the bulb to glow properly required resistance in series =R^ -R=440-240=200