The meter bridge is used to-

CONCEPT:

• Meter Bridge: It is an electrical 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, \(\frac{P}{Q} = \frac{R}{S} \Rightarrow S = \frac{{\left( {100\; - \;l} \right)}}{l}R\) Here S is unknown resistance that can be measured with the help of the meter bridge.

EXPLANATION:

• Thus the meter bridge is used to measure the resistance of a resistor. So option 3 is correct.