Question

Why is the balance point of the meter bridge experiment preferred to be taken in between 30 cm and 70 cm?

Answer 1

Wheatstone Bridge:

1. Wheatstone bridge is an electrical circuit that is used to measure the unknown resistance of a conductor.
2. It works on the principle of null deflection.

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In the above circuit $R_1,R_2,R_{s_{}}$are knows resistance whereas $R_x$ is an unknown resistance.

Here if the above-given condition is satisfied then the current passing through the galvanometer will be zero.

Then we can easily calculate the value of the unknown resistor $R_x$ by solving the above-given condition - $\frac{R_x}{R_2}=\frac{R_s}{R_1}$

=> $R_x=R_2\times \frac{R_s}{R_1}$

Meter Bridge:

1. It is an instrument that works on the principle of the Wheatstone bridge.
2. It is used to find the unknown resistance of a conductor as in a Wheatstone bridge.

Balance point in meter bridge:

The balance point in a meter bridge is that point on the meter wire at which deflection in the galvanometer is null.

Explanation:

1. In the meter bridge, the experiment balance point is preferred to be taken in between $30$ cm and $70$ cm in order to increase the sensitivity of the meter bridge. This will minimize the errors in measuring the value of unknown resistance.
2. If the null point of the meter bridge is far from the middle point, then the resistance of copper strips with unknown resistance has to be included. And at far points from the center, this unknown resistance is not negligible. So it will create errors in measuring the unknown resistance.
3. The connection between the resistors in the meter bridge is done using thick copper wires. Copper has very low resistivity. By using thick copper wires the resistivity is reduced further.

Thus, it is preferred to take a balance point between $30$ cm and $70$ cm in a meter bridge.