# 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

P Plabita

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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