The resistance of hot tungsten filament is about 10 times the cold resistance. What will be the resistance of 100 W and 200 V lamp when not in use?

  • Option 1)

    400\; \Omega

  • Option 2)

    200\; \Omega

  • Option 3)

    40\; \Omega

  • Option 4)

    20\; \Omega

 

Answers (2)

As we learnt in

if R=r -

P_{max}=\frac{E^{2}}{4r}

- wherein

Power delivered will be maximum

 

 P = VI = \frac{V^{2}}{R}

R_{hot} = \frac{V^{2}}{P}= \frac{200\times 200}{100}= 400\Omega

R_{cold}=\frac{400}{10}

            = 40\Omega

 


Option 1)

400\; \Omega

This option is incorrect.

Option 2)

200\; \Omega

This option is incorrect.

Option 3)

40\; \Omega

This option is correct.

Option 4)

20\; \Omega

This option is incorrect.

N neha

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