JCECE Medical JCECE Medical Solved Paper-2008

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

    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 \[\text{o }\!\!|\!\!\text{ =}\,\text{o}{{\text{ }\!\!|\!\!\text{ }}_{0}}+4t\] So, voltage across primary \[{{V}_{p}}=\frac{d\text{o }\!\!|\!\!\text{ }}{dt}=\frac{d}{dt}(o{{|}_{0}}+\,4t)\] \[=4V\,\](as \[\text{o}{{\text{ }\!\!|\!\!\text{ }}_{0}}=\]constant ) Also, we have \[{{N}_{p}}=50\]and \[{{N}_{s}}=1500\] From relation, \[\frac{{{V}_{s}}}{{{V}_{p}}}=\frac{{{N}_{s}}}{{{N}_{p}}}\] or \[{{V}_{s}}=\frac{{{V}_{p}}{{N}_{s}}}{{{N}_{p}}}\] \[=4\left( \frac{1500}{50} \right)\] \[=120\,V\] Note As in case of given transformer, voltage in secondary is increased, hence it is a step-up transformer.


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