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

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

Moving Charges and Magnetism

Solution:

Deflection current
$Ig_{max} = n \times k = 0.005 \times 30$
Where, n = Number of divisions = 30 and k = 0.005 amp/division
$=15\times 10^{-2} =0.15$
$v=I_{g}[20+R]$
$15=0.15 [20+R]$
$100=20+R$
$R=80\,\Omega$