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JEE Main 2019 (12 Apr, Shift 2) · Kirchhoff's Laws & Measuring Instruments

Kirchhoff's Laws & Measuring Instruments question from JEE Main 2019 (12 Apr, Shift 2)

Q166JEE Main 2019 · 12 APR · SHIFT 2Medium

Kirchhoff's Laws & Measuring Instruments

A moving coil galvanometer, having a resistance G, produces full scale deflection when a current Ig flows through it. This galvanometer can be converted into (i) an ammeter of range 0 to I0(I0 > Ig) by connecting a shunt resistance RA to it and (ii) into a voltmeter of range 0 to V (V = GI0) by connecting a series resistance RV to it. Then,

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Answer: (d)

  1. Ammeter shunt: RA=IgGI0−IgR_A = \frac{I_g G}{I_0 - I_g}
  2. Voltmeter series resistance: RV=VIg−G=GI0Ig−G=G(I0−Ig)IgR_V = \frac{V}{I_g} - G = \frac{G I_0}{I_g} - G = \frac{G(I_0 - I_g)}{I_g}
  3. Product: RARV=G2R_A R_V = G^2
  4. Ratio: RARV=(IgI0−Ig)2\frac{R_A}{R_V} = \left(\frac{I_g}{I_0 - I_g}\right)^2
  5. So the answer is (d).
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