The amount of heat (H) produced is given by the joule’s law of heating as H= Vlt
Current, I = 5 A
Time, t = 30 s
Voltage, V = Current x Resistance = 5 x 20 = 100V
H= 100 x 5 x 30 = 1.5 x 104 J.
Therefore, the amount of heat developed in the electric iron is 1.5 x 104 J.