A transformer connected to 220 V mains is used to light a lamp of rating 100 W and 110 V. If the primary current is 0.5 A, the efficiency of the transformer is (approximately)

Question

A transformer connected to 220 V mains is used to light a lamp of rating 100 W and 110 V. If the primary current is 0.5 A, the efficiency of the transformer is (approximately) (A) 60% (B) 35% (C) 50% (D) 90%

Tardigrade Admin · Accepted Answer

Key Concept Efficiency is defined as the ratio of output power and input power.
i.e.

η % = \frac{p _{o u t}}{p _{in}} \times 100

For an ideal transformer,

p_{out} = p_{in}

so,

η = 100%

but in practical, efficiency of transformer lies between

70 - 90%

.
Given,

V = 200 V, I_{p} = 0.5 A, P_{s} = 100 W

We know that,

P_{p} = V_{p} \cdot I_{P} = 220 \times 0.5

P_{p} = 110 W

η = \frac{P _{S}}{P _{p}}

Efficiency of the transformer,

= \frac{100}{110} = 0.9 or 90%

Q. A transformer connected to $220 V$ mains is used to light a lamp of rating $100 W$ and $110 V$ . If the primary current is $0.5 A$ , the efficiency of the transformer is (approximately)

60%

35%

50%

90%

44%

Q. A transformer connected to 220V mains is used to light a lamp of rating 100W and 110V. If the primary current is 0.5A, the efficiency of the transformer is (approximately)

60%

35%

50%

90%

44%

Q. A transformer connected to $220 V$ mains is used to light a lamp of rating $100 W$ and $110 V$ . If the primary current is $0.5 A$ , the efficiency of the transformer is (approximately)