Answer: (3) He should change S to 3Ω and repeat the experiment
The balance of a metre bridge is always maintained. The long wire in a metre bridge measures 1m = 100cm in length and is composed of constantan or manganin with a uniform cross-sectional area. The formulae that were employed in the solution are given here.
Meter bridge
A meter bridge also called a slide wire bridge is an instrument that works on the principle of a Wheatstone bridge. A meter bridge is used in finding the unknown resistance of a conductor as that of in a Wheatstone bridge. The devices required in finding the unknown resistance of a conductor using a meter bridge are:
- Meter bridge
- Resistance box
- Galvanometer
- Unknown Resistance of a length 1 m
- Screw gauge
- Connecting Wires
- Jockey
- One way key
How is a meter bridge used in finding the unknown resistance?
A meter bridge is an apparatus utilized in finding the unknown resistance of a coil. The below figure is the diagram of a useful meter bridge instrument.
In the above figure,
- R = Resistance
- P = Resistance coming across AB
- S = Unknown Resistance
- Q = Resistance between the joints BD
AC is the long wire measuring 1m in length and it is made of constantan or manganin having a uniform area of the cross-section such that
L1 + L2 = 100
Assuming that
- L1 = L
- L2 = 100 – L
Relation obtains the unknown resistance ‘X’ of the given wire:
X = RL2/L1
X = R(100 – L)/L
Given parameters
- S = 100Ω
- l1 = 2.9 cm
97.1R = 290
R = 290/97.1
R = 2.98Ω
2.98Ω ≈ 3Ω
The meter-bridge is of the same order, as a result, the student must use 3Ω to improve the accuracy of the measurement of resistance R.
