A step down transformer works on 220 volts a.c. mains. It is used to light a 100 w, 20 V bulb. The main current is 0.5 A. What is the efficiency of th
A step down transformer works on 220 volts a.c. mains. It is used to light a 100 w, 20 V bulb. The main current is 0.5 A. What is the efficiency of the transformer?
A. 0.91
B. 0.8
C. 0.71
D. 0.51
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Correct Answer - A
`I_(s) = W/V = 100/20 = 5A`
Efficiency `eta = (V_(s)I_(s))/(V_(p)I_(p)) = (20 xx 5)/(220 xx 0.5)`
`=100/110 = 91 %`
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