Question

A voltmeter and an ammeter are joined in series to an ideal cell, giving readings V and A respectively. If a resistance equal to the resistance of the ammeter if now joined in parallel to the ammeter

• A. V will no change
• B. V will increase slightly
• C. A will become exactly half of its initial vale
• D. A will become slightly more than half of its initial value

Answer 1

Answer: (B), (D)

The correct options are
B V will increase slightly
D A will become slightly more than half of its initial value

Let the voltage of the cell be $V$, resistance of the voltmeter be $r$ and the resistance of the ammeter be $R$.

Initially, the reading of the voltmeter=$V_1=\frac{V}{R+r}r$

Reading of the ammeter=$i_1=\frac{V}{R+r}$

Finally after connecting resistance in parallel to the ammeter, the reading of the voltmeter=$V_2=\frac{V}{r+\frac{R}{2}}r>V_1$

Reading of the ammeter=$\frac{1}{2}\frac{V}{r+\frac{R}{2}}=\frac{V}{2r+R}<i_1$