Question

An ammeter $A$ of finite resistance, and a resistor $R$ are joined in series to an ideal cell $C$. The ammeter reading is $I_0$ and the potentiometer reading is $V_0$. $P$ is now replaced by a voltmeter of finite resistance. The ammeter reading now is $I$ and the voltmeter reading is $V$.

• A. $I<I_0$, $V<V_0$
• B. $I>I_0$, $V=V_0$
• C. $I=I_0$, $V<V_0$
• D. $I<I_0$, $V=V_0$

Answer 1

The correct option is A $I<I_0$, $V<V_0$

The potentiometer is almost an ideal voltmeter, hence the resistance of potentiometer is infinity.
Current through potentiometer is very small, it does not draw any current from circuit. When the potentiometer is replaced by an voltmeter of finite resistance, the current through voltmeter is more than that of potentiometer. It means voltmeter draws some current from circuit.

Hence, $I<I_0$

Also, $V=IR$, Hence, $V<V_0$