Question

A transformer is used to light a 0W - 110V lampfrom 220 mains. If main current is 0.25 A, efficiency of transformer is :
91%
95%
96%
99%​

Answer 1

The efficiency of the transformer is 181%

Given Data

Main voltage = 220V

Main curent = 0.25A

Voltage of lamp = output= 110V

Power of light = 100W

To calculate

The efficiency of the transformer

Calculation

Efficiency = output/ input x100

Efficiency = 100/(220x 0.25) x 100 = 181%

Conclusion

None of the option is correct

Answer 2

Efficiency of the transformer is 91% if A transformer is used to light a 50W - 110V lamp from 220 mains and  main current is 0.25 A

Given:

• A transformer is used to light a 50W - 110V lamp from 220 mains
• Main current is 0.25 A

To Find:

• Efficiency of transformer

Solution:

• Efficiency of transformer in % = (Output Power / Input Power) x 100
• Power = Voltage x Current

Step 1:

Calculate Input power.

Input power = 220 x 0.25

Input power = 55 W

Step 2:

Output power is 50 W hence Calculate Efficiency

Efficiency = (50/55) x 100  %

Efficiency = 1000/11  %

Efficiency ≈ 90.91 %

From the given options 91% is closest

Hence ,  efficiency of the transformer is 91%

( Question mention 0W , which is not possible probably correct Question is 50 W)