Question

shows a 240 V ac mains circuit to which a number of appliances are connected and
Figure
switched on.
240 ac
Fan
1.2 kW
Refrigerator
200 W
60 W
60 W
a) Calculate the power supplied to the circuit.
b) Calculate
(i) the current in the refrigerator,
(ii) the energy used by the fan in 3 hours,
(iii) the resistance of the filament of one lamp.
​

Answer 1

Power used by Fan = 1200 W

Power used by Refrigerator = 200 W

Power used by two bulbs = 120 W

Total Power = 1520 W

2. (a) current in refrigerator = 200/240 = 5/6 A = 0.833 A

2. (b) Energy used by fan in 3 hours = 1.2 kW×3 hr= 3.6 kW-hr

= 1200×3×60×60 = 12.96 MJ

2. (c) Resistance of filament P = V2/R or R = V2 / P = 240×240 / 60 = 960 Ω