Question

 A resistance of 40 ohms and one of 60 ohms are arranged in series across 220 volt supply. Find the heat in joules produced by this combination of resistances in half a minute.

Answer 1

 The net resistance of the circuit, R = 40 + 60 = 100 
Time for which current is passed =  `1/2 minute =30s` minute = 30 s
Current in the circuit = `V/R=220/100 =2.2 A`
Heat produced = I²Rt = (2.2)² (100) (30) = 4.84 x 100 x 30 = 14520 J