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NEET Physics Alternating Current / प्रत्यावर्ती धारा NEET PYQ-Alternating Current

  • question_answer
    A series LCR circuit is connected to an ac voltage source. When L is removed from the circuit, the phase difference between current and voltage is \[\frac{\pi }{3}\]. If instead C is removed from the circuit, the phase difference is again \[\frac{\pi }{3}\]between current and voltage. The power factor of the circuit is:                        [NEET 2020]

    A)  0.5                  

    B)  1.0

    C)  -1.0                 

    D)       zero

    Correct Answer: B

    Solution :

    [b] When L is removed,
                \[\tan \phi =\frac{\left| {{X}_{C}} \right|}{R}\Rightarrow \tan \frac{\pi }{3}=\frac{{{X}_{C}}}{R}\]            …(i)
                When C is removed,
                \[\tan \phi =\frac{\left| {{X}_{L}} \right|}{R}\Rightarrow \tan \frac{\pi }{3}=\frac{{{X}_{L}}}{R}\]            …(ii)
    From (i) and (ii), \[{{X}_{L}}={{X}_{C}}\]
    Since, \[{{X}_{L}}={{X}_{C}}\], the circuit is in resonance.
                            \[Z=R\]
    Power factor \[=\cos \phi =\frac{R}{Z}=1\]


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