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NEET Physics Electro Magnetic Induction NEET PYQ-Electro Magnetic Induction

  • question_answer
    The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux \[\phi \] linked with the primary coil is given by \[\phi ={{\phi }_{0}}+4t,\] where \[\phi \] is in weber, t is time in second and \[{{\phi }_{0}}\] is a constant, the output voltage across the secondary coil is: [AIPMT (S) 2007]

    A)  90 V    

    B)                   120 V

    C)  220 V    

    D)                  30 V

    Correct Answer: B

    Solution :

    The magnetic flux linked with the primary coil is given by
                            \[\phi ={{\phi }_{0}}+4\,t\]
                So, voltage across primary
                            \[{{V}_{P}}=\frac{d\phi }{dt}=\frac{d}{dt}({{\phi }_{0}}+4t)\]
                            = 4 volt            (as \[{{\phi }_{0}}=\] constant)
                Also, we have
                            \[{{N}_{p}}=50\] and \[{{N}_{s}}=1500\]
                From relation,
                            \[\frac{{{V}_{s}}}{{{V}_{p}}}=\frac{{{N}_{s}}}{{{N}_{p}}}\]
                or         \[{{V}_{s}}={{V}_{p}}\frac{{{N}_{s}}}{{{N}_{p}}}\]
                            \[=4\left( \frac{1500}{50} \right)\]
                            \[=120\text{ }V\]
    Note:    As in case of given transformer, voltage if secondary is increased, hence it is a step-up transformer.


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