Question

A bulb is marked 150 W - 220 V and an electric heater is marked 1500 W - 220 V. What is the ratio of resistances of these two devices?​

Answer 1

Answer

A bulb is marked 150 W - 220 V and an electric heater is marked 1500 W - 220V. The ratio of resistances of these two devices is

Explanation: we can take R1 as the resistance of the bulb filament and R2 as the resistance heater.

P = V×I

I = V/R

P = 150w

150 = 220 × I = 220 × V/ R1 = 220×220/R1

Hence, R1 = 220×220/ 150 = 322.6 ohm

For heater,

1500 = 220×I = 220×V/R2 = 220×220/R2

R2 = 220×220/1500 = 32.26 ohm

ie, R1:R2 = 10:1