Explanation:

In the measurement of resistance by a meter bridge, the current is necessarily reversed through the bridge wire to eliminate end errors.

What is a Meter Bridge:
A meter bridge is a device used to measure the unknown resistance of a conductor. It consists of a long uniform wire AB, known as the meter wire, which is mounted on a wooden base. The wire is stretched between two fixed terminals, C and D, which are connected to a power supply. A jockey is used to make contact with the wire at different points.

Working Principle of a Meter Bridge:
The working principle of a meter bridge is based on the principle of Wheatstone bridge. When a known resistance (R) and an unknown resistance (X) are connected in the two arms of the bridge, and a galvanometer is connected between the junction points, the bridge is said to be balanced when no current flows through the galvanometer. At this point, the ratio of the known resistance to the unknown resistance is equal to the ratio of the two arms of the bridge.

End Errors:
End errors occur due to the imperfect contact between the jockey and the wire at the ends of the meter bridge. These errors can lead to inaccurate resistance measurements. When the current is passed in only one direction through the bridge wire, the end errors can cause a significant difference in the resistance measurements.

Reversing the Current:
To eliminate the end errors, the current is reversed through the bridge wire. This means that the direction of the current is changed, and it is passed in the opposite direction through the wire. By reversing the current, any end errors that were present in the first measurement are canceled out by the end errors in the second measurement. This helps to eliminate the systematic errors and provides a more accurate measurement of the resistance.

Eliminating End Errors:
When the current is reversed, any end errors that were present in the first measurement will be reversed in the second measurement. This is because the jockey is now making contact with a different part of the wire. By taking the average of the two measurements (one with current in one direction and the other with current in the opposite direction), the end errors can be eliminated. This ensures a more accurate measurement of the unknown resistance.

Therefore, in the measurement of resistance by a meter bridge, the current is necessarily reversed through the bridge wire to eliminate end errors.