For a metre bridge, choose the incorrect option from the following.

The correct answer is Option (4) → The internal resistance of the cell affects the balancing position of null point.

A metre bridge is a Wheatstone bridge whose two arms are parts of a uniform wire. At the null point no current flows through the galvanometer, and the balance condition contains only the four resistances:

    \( \displaystyle \frac{X}{Y} = \frac{R_{l_1}}{R_{l_2}} = \frac{l_1}{l_2} \)

Option (1) The wire of one metre length fixed on the wooden plank is a uniform conducting wire having constant resistance per unit length. — True statement. Only a uniform wire lets the ratio of lengths replace the ratio of resistances.

Option (2) Metre bridge is not suitable to measure very low resistances. — True statement. For a very low resistance, the resistances of the leads and contacts are comparable with it, so the error is large.

Option (3) Interchanging the position of the galvanometer and the cell will not change the balance point on the wire \( X/Y = l_1/l_2 \). — True statement. Interchanging them leaves the balance condition, and so the null point, unchanged.

Option (4) The internal resistance of the cell affects the balancing position of null point. — False statement, so this is the answer. The balance condition does not contain the cell; its internal resistance changes only the current through the wire.