The balance point in the meter bridge is obtained:

CONCEPT:

• Meter bridge: Meter bridge is instruments based on the principle of Wheatstone bridge and is used to measure an unknown resistance.
• In the case of a meter bridge, the resistance wire AC is 100 cm long. Varying the position of tapping point B, the bridge is balanced.
• If in the balanced position of bridge AB = l, BC (100 – l) so that

\(\frac{Q}{P} = \frac{{\left( {100 - l} \right)}}{l}\)

Also, \(\frac{P}{Q} = \frac{R}{S} \Rightarrow S = \frac{{\left( {100 - l} \right)}}{l}R\)

EXPLANATION:

• When the balance point is in the middle of the bridge wire, the resistance in the four arms P, Q, R, and S become of the same order and consequently the bridge becomes more sensitive.
• Thus, the balance point is obtained in the middle of the meter bridge wire. Therefore option 4 is correct.