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  • I need help with A resistance 'R' draws power 'P' when connected to an AC source. If an inductance is now placed in series with the resistance, such that the impedance of the circuit becomes 'Z', the power drawn will be:

A resistance 'R' draws power 'P' when connected to an AC source. If an inductance is now placed in series with the resistance, such that the impedance of the circuit becomes 'Z', the power drawn will be:

  • Option 1)

    P(\frac{R}{Z})^{2}

  • Option 2)

    P

  • Option 3)

    P\sqrt (\frac{R}{Z})

  • Option 4)

    P(\frac{R}{Z})

 

Answers (1)

best_answer

As we learnt in 

Average power (True power) -

P_{av}= V_{rms}: : i_{rms}cos phi

-

 

 case I : P=V_{rms}\times I_{rms}

                  =V_{rms}\times \frac{V_{rms}}{R}    

P= \frac{V_{rms}^{2}}{R}\Rightarrow V^{2}_{rms}=PR

case II : power drawn in LR circuit

P'=V_{rms}\times I_{rms}\cos\phi=V_{rms}\times \frac{V_{rms}}{Z}\times \frac{R}{Z}

P'= V^{2}_{rms}\frac{R}{Z^{2}}=PR\times \frac{R}{Z^{2}}

\therefore P'=\frac{PR^{2}}{Z^{2}}


Option 1)

P(\frac{R}{Z})^{2}

Correct

Option 2)

P

Incorrect

Option 3)

P\sqrt (\frac{R}{Z})

Incorrect

Option 4)

P(\frac{R}{Z})

Incorrect

Posted by

prateek

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