NEET Physics Electro Magnetic Induction NEET PYQ-Electro Magnetic Induction

  • question_answer
    A transformer is used to light a 100 W and 110 W lamp from a 220 W mains. If the main current is 0.5 A, the efficiency of the transformer is approximately:                      [AIPMT (S) 2007]

    A)              30%

    B)                   50%    

    C)              90%      

    D)                   10%

    Correct Answer: C

    Solution :

    The efficiency of transfer
                \[\text{=}\frac{\text{Energy}\,\text{obtained}\,\text{from}\,\text{the}\,\text{secondary}\,\text{coil}}{\text{Energy}\,\text{given}\,\text{to}\,\text{the}\,\text{primary}\,\text{coil}}\]
    or         \[\eta \text{=}\frac{\text{Output}\,\text{power}}{\text{Input}\,\text{power}}\]
    or         \[\eta =\frac{{{V}_{s}}{{I}_{s}}}{{{V}_{p}}{{I}_{p}}}\]
    Given,  \[{{V}_{s}}{{I}_{s}}=100\,W,\,{{V}_{p}}=220\,\,V,\,{{I}_{p}}=0.5\,A\]
    Hence,  \[\eta =\frac{100}{220\times 0.5}=0.90=90%\]


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