Question

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

1) 50%

2) 90%

2) 10%

4) 30%

Answer 1

Efficiency of the transformer is 90.91%

Solution:

The transformer has input power and an output power. Input power is based on the main current drawn into the circuit.  

Ratio of output power to input power gives the efficiency, which is calculated as follows,

Given:  Voltage V = 220 V Current I = 0.5 A   Output Power = 100 W

Input Power = Voltage $\times$  Current

Input Power = $220 \times 0.5$  

Input power = 110 W

As we know that efficiency, Efficiency = Input Power / Output power $\times$ 100%

$\eta=\frac{100}{110} \times 100 \%$

ƞ=90.91 %