Question

The resistance of an ammeter is $13\Omega$ and its scale is graduated for a current upto $100A$ . After an additional shunt has been connected to this ammeter, it becomes possible to measure currents upto $750A$ by this meter. The value of shunt resistance is

• A. $20\Omega$
• B. $2\Omega$
• C. $0.2\Omega$
• D. $2k\Omega$

Answer 1

Answer: (B)

Lets suppose we have introduced a shunt resistance $R_{sh}$ in parallel with ammeter resistance $R$ , the current through ammeter resistance is $I$ and the current through shunt resistance is $I_{sh}$ . It is given that $I=100A$ and the total current is $750A$ , So $I_{sh}=750A-100A=650A$ . Now both the resistance are connected in parallel hence $IR=I_{sh}{R}_{sh}$ $\Rightarrow 100\times 13=650\times R_{sh}$ $\Rightarrow R_{sh}=2ohm$