Page 23 - Physics - XII

Verifi cation
Experimental value of parallel combination = X = _____ Ω
P
XX
Theoretical value of parallel combination, X 1 2
p X X
Error 1 2
The error in the experimental value of X can be estimated as
P
l l '
∆X = X P , l' = 100 – l
P l '
l
∆l and ∆l' indicate the least count of the measuring scale on the metre bridge.

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

Precautions
Same as experiment 3(a).

Sources of Error
Same as experiment 3(a).

VIVA VOCE

Q1. What is the other name used for metre bridge?
Ans. Slide wire bridge

Q2. What is the condition for a Wheatstone bridge to become balanced?

Ans. P = R
Q S

Q3. Why the jockey should not be pressed too hard on the wire when sliding over it?
Ans. If done so, it would damage the uniformity of the bridge wire.
Q4. How will the sensitivity of metre bridge change under following condition?

Rheostat head is moved from minimum resistance to maximum resistance positions. (NCERT)
Ans. If the rheostat head is at the minimum resistance position, then the order of known resistance may
be less than that of other resistance. So, the bridge is less sensitive.

If the rheostat head is at the middle resistance position, then the order of known resistance may be
same as that of other resistance. So, the bridge is more sensitive.
If the rheostat head is at the maximum resistance position, then the order of known resistance may
be more than that of other resistance. So, the bridge is less sensitive.
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