The resistance of an ammeter is $13 \Omega$ and its scale is graduated for a current upto 100 amps. After an…

The resistance of an ammeter is $13 \Omega$ and its scale is graduated for a current upto 100 amps. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto 750 amperes by this meter. The value of shunt-resistance is:
  1. $2 \Omega$
  2. $0.2 \Omega$
  3. $2 \mathrm{k} \Omega$
  4. $20 \Omega$

Solution

Let the shunt resistance be S.

\(\begin{aligned} & \text {Given: } I=750 \mathrm{~A}, \\ & I_g=100 \mathrm{~A}, R_G=13 \Omega \\ & \text {From the figure, } \\ & I_g R_G=\left(I-I_g\right) S \\ & \text {or } 100 \times 13=[750-100] S \\ & \text {or } 1300=650 \mathrm{~S} \\ & \therefore \quad S=1300 / 650=2 \Omega .\end{aligned}\)

Asked in: NEET 2007

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