Question

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

• A. $20\,\Omega$
• B. $2\,\Omega$
• C. $0.2\,\Omega$
• D. $2\,k\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 $I=100\,A$ and the total current is $750\,A$ , So $I_{sh}=750\,A-100A=650A$ . Now both the resistance are connected in parallel hence $IR=I_{sh}R_{sh}$ $\Rightarrow 100\times 13=650\times R_{sh}$ $\Rightarrow R_{sh}=2\,ohm$