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A transformer is used to light 100 W 25 volt lamp from 250 Volt ac mains. The current in the main cable is 0.5 A. Calculate the efficiency of the transformer.
  • a)
    50%
  • b)
    60%
  • c)
    90%
  • d)
    80%
Correct answer is option 'D'. Can you explain this answer?
Most Upvoted Answer
A transformer is used to light 100 W 25 volt lamp from 250 Volt ac mai...
Given data:
Power of the lamp, P= 100 W
Voltage of the lamp, V = 25 V
Input voltage, V1 = 250 V
Input current, I1 = 0.5 A

To find: Efficiency of the transformer

Formula used:

Efficiency of transformer, η = Output power/Input power

Output power = VI
Input power = V1I1

Calculation:

Output voltage, V2 = V = 25 V

Output current, I2 = P/V = 100/25 = 4 A

Output power = VI = 25 × 4 = 100 W

Input power = V1I1 = 250 × 0.5 = 125 W

Efficiency of the transformer, η = Output power/Input power = 100/125 = 0.8 or 80%

Therefore, the efficiency of the transformer is 80%.
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Community Answer
A transformer is used to light 100 W 25 volt lamp from 250 Volt ac mai...
Given: Output power (Po) = 100 W; Ip = 0.5 A; Vp = 250 V
Input power (Pi) = Vp × Ip
Pi = 250 × 0.5 = 125 W
Efficiency = (Output power/Input power) × 100%
Efficiency = (100/125) x 100
Efficiency = 80
Therefore, the efficiency of the transformer is 80%.
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