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  • How to solve this problem- - A galvanometer having a resistance of 20 and 30 divisions on both sides has figure of merit 0.005 a - Experimental skills - JEE Main

A galvanometer having a resistance of 20 \Omega and 30 divisions on both sides has figure of merit 0.005 ampere/division. The resistance that should be connected in series such that it can be used as a voltmeter upto 15 volt, is :

  • Option 1)

     80 \Omega

  • Option 2)

    120 \Omega

  • Option 3)

    100 \Omega

  • Option 4)

    125 \Omega

Answers (1)

best_answer

 

To determine the resistance of a galvanometer by half deflection method -

G= \frac{RS}{R-S}

G= galvanometer resistance 

R= External resistance

S= Shunt

Procedure

Resistance of galvanometer by half deflection method.

1.    Draw the circuit diagram as shown in figure.

2.    See that plugs of the resistance boxes are tight.

3.    Take out high resistance (2000 \Omega) from the resistance box R and insert the key K1 only.

4.    Adjust the value of R so that deflection is maximum, even in number and within scale. 

5.    Note the deflection. Let it be \theta.

6.    Now, insert the key K2 and without changing the value of R adjust the value of S such that deflection in the galvanometer reduces to exactly half the value obtained in step 5 i.e. \frac{\theta}{2}

7.    Note the value of resistance S.

8.    Repeat steps 4 to 7 three times taking out different values of R and adjusting S every time. 

- wherein

I_{g}\propto \theta

I_{g}=K \theta

\theta= definite angle

Ig  = current passing through galvanometre

K= figuring merit

 

 


Option 1)

 80 \Omega

Option 2)

120 \Omega

Option 3)

100 \Omega

Option 4)

125 \Omega

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