A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A , the efficiency of the transformer is approximately

Step-by-step solution

The efficiency of transformer = Energy obtained from the secondary coil Energy given to the primary coil or array lrl or & & = Output power Input power or & & = V_s I_s V_p I_p Given, & V_s I_s & =100 ~W , V_p=220 ~V , I_p=0.5 ~A Hence, & & = 100 220 0.5 =0.90=90 % array