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Moving Charges and Magnetism — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsMoving Charges and Magnetism5 Marks
Question
A multirange current meter can be constructed by using a galvanometer circuit as shown in Fig. We want a current meter that can measure $10mA,$ $100mA$ and $1A$ using a galvanometer of resistance $10\Omega$ and that prduces maximum deflection for current of $1mA.$ Find $S_1, S_2$ and $S_3$ that have to be used.
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Answer

Key concept: A galvanometer can be converted into ammeter by connecting a very low resistance wire (shunt S) connected in parallel with galvanometer. The relationship is given by $I_gG = (l - I_g) S,$ where $I_g$ is
the range of galvanometer, G is the resistance of galvanometer.

For measuring $I_1 = 10mA : IG.G = (I_1 - IG)(S_1 + S_2 + S_3)$
For measuring $I_2 = 100mA : IG(G + S_1) = (I_2 - IG)(S_2 - S_3)$
For measuring $I_3 = 1A : IG(G + S_1 + S_2) =(I_3 - IG)(S_3)$
Gives $S_1 = 1\Omega , S_2 = 0.1\Omega$ and $S_3 = 0.01\Omega .$

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