A transformer is used to light 140 W, 24 V lamp from a 240 V ac mains. If the main current is 0.7 A, the efficiency of the transformer is

Question

A transformer is used to light 140 W, 24 V lamp from a 240 V ac mains. If the main current is 0.7 A, the efficiency of the transformer is (A) 63.8 % (B) 74 % (C) 83.3 % (D) 48 %

Tardigrade Admin · Accepted Answer

Output power = 140 W Input power = 240 × 0.7 = 168 W Efficiency =(output power/input power)×100 =(140/168)×100 =83.3 %

Q. A transformer is used to light $140 W$ , $24 V$ lamp from a $240 V$ ac mains. If the main current is $0.7 A$ , the efficiency of the transformer is

$63.8%$

$74%$

$83.3%$

$48%$

Output power $= 140 W$
Input power $= 240 \times 0.7 = 168 W$
Efficiency $= \frac{o u tp u t p o w er}{in p u t p o w er} \times 100$
$= \frac{140}{168} \times 100$
$= 83.3%$

Q. A transformer is used to light 140W, 24V lamp from a 240V ac mains. If the main current is 0.7A, the efficiency of the transformer is

63.8%

74%

83.3%

48%