Alternating CurrentHard

Question

A transformer is used to light a 140 watt, 24 volt lamp from 240 V AC mains. The current in the main cable is 0.7 amp. The efficiency of the transformer is :

Options

A.48 %
B.63.8 %
C.83.8 %
D.90 %

Solution

η% = × 100    = × 100 = 83.3%.

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