Page 17 - Physics - XII

Observations
Table for the unknown resistance

S. Resistance from Length Length Unknown resistance
No. the resistance box AD = l DC = (100 – l) l
Q (Ω) (cm) (cm) X l Q
100
(Ω)
1.

2.
3.

4.
X + X + X + X
Mean resistance X = 1 2 3 4 = _____ Ω.
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Result

The value of unknown resistance X is _____ Ω.

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.

VIVA VOCE

Q1. Which has higher resistance — a thin wire or a thick wire of the same material and same
length?
Ans. Thin wire

Q2. What are the factors on which resistance of a conductor depends?
Ans. (i) Resistance of a conductor is proportional to the length of the conductor.

(ii) Resistance of a conductor is inversely proportional to the area of cross-section of the conductor.
Q3. What is the eff ect of temperature on the resistance of the conductor?
Ans. Resistance of conductor increases with the rise of temperature.

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