Shown in the figure below is a meter­bridge set up with null deflection in the galvanometer. The value of the unknown resistance  R is :

  • Option 1)

    55\Omega

  • Option 2)

    13.75 \Omega

  • Option 3)

    220 \Omega

  • Option 4)

    110 \Omega

 

Answers (1)

As we learnt in

Wheat stone Bridge -

It is an arrangement of four resistances which can be used to measure one of them in terms of rest

- wherein

 

 

 

This is a Wheatstone bridge.

If   \rho _{l}   is the resistance per unit length (in cm)

\frac{20\rho _{l}}{55}= \frac{80\rho _{l}}{R}\: \: or \: \: R= \frac{80\times 55}{20}= 220\Omega


Option 1)

55\Omega

This option is incorrect.

Option 2)

13.75 \Omega

This option is incorrect.

Option 3)

220 \Omega

This option is correct.

Option 4)

110 \Omega

This option is incorrect.

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