The meter bridge works on the principle of

• Wheatstone Bridge: In the below diagram, BD is Wheatstone Bridge when there is no current across it. This happens when

\(\frac{R_1}{R_3} = \frac{R_2}{R_4}\)

• Meter Bridge: It is an electrical instrument used to measure an unknown resistance.
• It works on two principles, one is Wheatstone Bridge, and the other is 'direct proportionality relationship between length and resistance of a wire.'

• Working of meter Bridge: AC is long resistance wire 100 cm long.. Varying the position of tapping point B, the bridge is balanced.
• Bridge Balanced means the galvanometer is showing zero resistance and the condition satisfying wheatstone Bridge.
• If B is the balanced position of bridge AB = l, BC (100 – l) so that

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

Also, By condition of Wheatstone Bridge.

\(\frac{P}{Q} = \frac{R}{S}\)

⇒ \(S = \frac{{\left( {100\; - \;l} \right)}}{l}R\) 

Here S is unknown resistance that can be measured with the help of the meter bridge. 

Hence, we can say that the meter bridge works on the principle of Wheatstone Bridge and direct proportionality relationship between length and resistance of a wire.'

So, the correct option is Both (1) and (2)