Question

By mistake, a voltmeter is placed in series and an ammeter is parallel with a resistance in an electric circuit, with a cell in series.

• A. If the devices are ideal, ammeter will read zero current and voltmeter will read the emf of cell.
• B. If the devices are ideal, a large current will flow through the ammeter, and it will be damaged.
• C. The main current in the circuit will be very low, and practically all current will flow through the ammeter if the resistance of the ammeter is much smaller than the resistance in parallel.
• D. The devices may get damaged if emf of the cell is very high and the meters are not ideal.

Answer 1

Answer: (A), (C), (D)

The devices may get damaged if emf of the cell is very high and the meters are not ideal.

Ideal voltmeter has infinite resistance, $R_V=\infty$.

Ideal ammeter has almost zero resistance, $R_A=0$.

If devices are ideal, then $R_V=\infty$ and current through this circuit will be zero.
Ammeter will read zero current and voltmeter will read the voltage of the battery.

If devices are not ideal then very small current will flow through the circuit. Good ammeter has very small resistance compared to other resistors in the circuit. Hence, it will act as short circuit and almost all current will flow through it.

If current is higher than maximum deflection current, then devices may get damaged. This can happen when EMF of the cell is very high.

Hence, options $\text{(A), (C)}$ and $\left(\text{D}\right)$ are correct.