Chapter 29, Problem 1PLA

To determine

The true statement when the Wheatstone bridge is balanced.

Answer to Problem 1PLA

Option (b), (c), (e) and (f). There is no current in the galvanometer, there is no voltage drop across the galvanometer, the currents in $R_1$ and $R_2$ are the same and the voltage across $R_1$ and $R_2$ is the same.

Explanation of Solution

Wheatstone bridge is balanced when there is no current flowing through the galvanometer and the potential difference across the point $A$ and $B$ is zero.

The main use of the balanced Wheatstone bridge is to measure the unknown resistance of the resistor connected to the circuit.

Equation that obeys when the bridge is balanced is

    $\frac{R_1}{R_2}=\frac{R_3}{R_4}$

Where, $R_1,R_2,R_3\&R_4$ are the resistance of the resistors connected in the bridge circuit.

Conclusion:

1. (a) Current flows through the unknown resistor. Thus, option (a) is incorrect.
2. (b) No current flows through the galvanometer. Thus, option (b) is correct.
3. (c) No current across the galvanometer. Therefore, no voltage drops across the galvanometer. Thus, option (c) is correct.
4. (d) The current through $R_1$ and $R_2$ is the same. Thus, option (d) is incorrect.
5. (e) The current through $R_1$ and $R_2$ is the same. Thus, option (e) is correct.
6. (f) The voltage across $R_1$ and $R_3$ is the same. Thus, option (f) is correct.
7. (g) The voltage across $R_1$ and $R_2$ is the not same. Thus, option (g) is incorrect.