A transformer is used to light a 40 W, 10 V lamp from a 200 V mains supply. If the main primary curr

Question

A transformer is used to light a 40 W, 10 V lamp from a 200 V mains supply. If the main primary current is 0.25 A, the efficiency of the transformer is exactly

Professor PC Thomas Classes · Answer

(b) : The output power required to light the lamp is $P_{out} = 40$ W. The input power drawn from the mains is $P_{in} = V_p 	imes I_p = 200 	imes 0.25 = 50$ W. The efficiency of the transformer is given by $\eta = (P_{out}/P_{in}) 	imes 100\% = (40/50) 	imes 100\% = 80\%$.