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12th Class Physics Alternating Current / प्रत्यावर्ती धारा Question Bank MCQ - Alternating Currents

  • question_answer
    A transformer is used to light 140 W, 24 V lamp from a 240V AC mains. If the main current is 0.7 A, the efficiency of the transformer is:

    A) 63.8%                          

    B) 74%   

    C) 83.3%                          

    D) 48%

    Correct Answer: C

    Solution :

    (c) 83.3% Output power \[=140\text{ }W\] Input power \[=240\times 0.7=168\text{ }W\] \[\text{Efficiency=}\frac{\text{output}\,\,\text{power}}{\text{input}\,\,\text{power}}\text{ }\!\!\times\!\!\text{ 100}\]             \[\text{=}\frac{140}{168}\times 100=83.3%\]


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