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Question
State any two sources of errors in the meter-bridge experiment. Explain how they can be minimized.
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Solution 1
The chief sources of error in the meter bridge experiment are as follows:
- The cross-section of the bridge wire may not be uniform. The wire's resistance will not be proportional to its length since it will not have a consistent resistance per unit length.
- End resistances at the wire's two ends may be introduced as a result of:
- The resistance of the metal strips
- The contact resistance of the bridge wire with the metal strips
- The unmeasured lengths of the wire at the ends are because the contact points of the wire with the metal strips do not coincide with the two ends of the metre scale attached.
Such errors are almost unavoidable, but can be minimized considerably as follows:
- Readings must be taken by modifying the standard known resistance to obtain the null point close to the wire's centre. The null points should be in the middle one-third of the wire when taking multiple readings.
- The measurements must be repeated with the standard resistance (resistance box) and the unknown resistance swapped in the gaps of the bridge, and the averages of the two results obtained.
Solution 2
Sources of errors:
- The cross-section of the wire may not be uniform.
- The ends of the wire are soldered to the metallic strip where contact resistance is developed, which is not taken into account.
- The measurements of lx and lR may not be accurate.
To minimize the errors
- The value of R is so adjusted that the null point is obtained around the middle one-third of the wire (between 34 cm and 66 cm) so that percentage error in the measurement of lx and lR is minimum and nearly the same.
- The experiment is repeated by interchanging the positions of unknown resistance X and known resistance box R.
- The jockey should be tapped on the wire and not slid. The jockey is used to detect whether there is a current through the central branch. This is possible only by tapping the jockey.
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