SATHEE: Current Electricity 4 Question 8

Current Electricity 4 Question 8

8. A galvanometer having a resistance of $20 Ω$ 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

(2019 Main, 11 Jan II)

(a) $100 Ω$

(b) $125 Ω$

(d) $80 Ω$

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Solution:

Resistance of galvanometer, $(G) = 20 Ω$

Number of divisions on both side $= 30$

Figure of merit $= 0.005$ ampere/division

$∴$ Full scale deflection current $(I_{g})$

$=$ Number of divisions $\times$ figure of merit

$\Rightarrow I_{g} = 30 \times 0.005 = 0.15 A$

Now, for measuring $15 V$ by this galvanometer, let we use a resistance of $R$ ohm in series with the galvanometer.

$∴$ Effective resistance of voltmeter, $R_{eff} = R + 20$

As,maximum potential measured by voltmeter.

$\begin{aligned} V = I_{g} \cdot R_{eff} or 15 = 0.15 (R + 20) \\ R + 20 = 100 or R = 80 Ω \end{aligned}$

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Current Electricity 4 Question 8

8. A galvanometer having a resistance of 20Ω 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

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8. A galvanometer having a resistance of $20 Ω$ 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