A moving coil galvanometer has 150 equal divisions. Its current sensitivity is 10 divisions per milliampere and voltage sensitivity is 2 divisions per millivolt. In order that each division reads 1 volt, the resistance in ohms needed to be connected in series with the coil will be

  • Option 1)

    99995

  • Option 2)

    9995

  • Option 3)

    103

  • Option 4)

    105

 

Answers (1)

As we learnt in

Moving coil galvanometer -

It is a very sensitive instrument used to measure the small current.Galvanometer gives the deflection which is proportional to electric current flowing through it.

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V_{max}=\frac{150}{2}=75\, m\, V

I_{max}=\frac{150}{10}=15\, mA=I_{g}

Resistance of galvanometer  G=75/15=5\, \Omega

For conversion into a voltmeter, a high resistance should be connected in series with the galvanometer

V=I_{g}(G+R)=\frac{15}{1000}(5+R)\Rightarrow 150=15\frac{(5+R)}{1000}

or  5+R=\frac{150\times 1000}{15}=10000

\therefore \; \; \; R=9995\, \Omega


Option 1)

99995

Incorrect option

Option 2)

9995

Correct option

Option 3)

103

Incorrect option

Option 4)

105

Incorrect option

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