An electric heater which is connected to a 220 V supply line has two resistance coils A and B of 24 W resistance each. These coils can be used separately (one at a time) , in series or in parallel. Calculate the current drawn when : (a) only one coil (b) Coil A and B are used

Given V=220 V

R_A = R_B = 24 ohm

(a) Current drawn when only coil A is used:

I = V/R_A = 220/24

=9.16 amps

(b) Current drawn when coils A and B are used in series:

Total resistance, R = R_A + R_B = 24 + 24 = 48 ohms

I = V/R = 220/48

= 4.58 amps

(c) Current drawn when coils A and B are used in parallel:

Total resistance, 1/R = 1/R_A + 1/R_B = 1/24 + 1/24 = 2/24 = 1/12

R=12 ohms

I = V/R = 220/12

=18.33 amps