Page 21 - Physics - XII

Verifi cation
Series resistance by experiment = X = _____ Ω
S
Series resistance by theoretical formula X′ = X + X = _____ Ω
S 1 2
Error
The error in the experimental value of X can be estimated as
S
l l '
∆X = X S , l' = 100 – l
S l '
l
∆l and ∆l' indicate the least count of the measuring scale on the metre bridge.

Result
Theoretically expected value = X + X = _____ Ω
1 2
Experimentally obtained value = X ± ∆X = _____ Ω
S S
Within the limits of experimental error, the experimental and theoretical values of equivalent resistance for
the series combination of X and X are nearly equal. Hence, the law of combination of resistances (series)
2
1
is verifi ed.
Precautions

1. All the connections should be neat, clean, and tight.
2. All the plugs in the resistance box should be tight.

3. Null point should be taken between 30 and 70 cm.
4. The plug in key K should be inserted only when the observations are to be taken.
5. Move the jockey gently over the metre bridge wire.
6. The wire should not make a loop.

Sources of Error

1. The plugs may not be clean.
2. The wire may not have uniform area of cross-section.
3. Instrument screws may be loose.

EXPERIMENT - 3(b)

Aim

To verify the laws of combination (parallel) of resistances using a metre bridge.

Apparatus and Materials Required
A metre bridge, two diff erent resistances, a resistance box, a one-way key, a jockey, a sensitive galvanometer,
a cell, sand paper, and connecting wires

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