Page 53 - Physics - XI

3. The spinning of the bob cannot be completely avoided.

4. The air current may disturb the vibration.
5. There may be some personal error in starting and stopping the stopwatch.
6. The stopwatch may be inaccurate.

7. There may be a relative motion between the bob and the string.

EXPERIMENT - 8
Aim

To study variation of time period of a simple pendulum of a given length by taking bobs of same size but
diff erent masses and interpret the result.

Apparatus and Materials Required

Clamp stand, split cork, Vernier Calliper, stopwatch, strong cotton thread/string, fi ve metallic bobs of
diff erent masses (50 g, 75 g, 100 g, 125 g, 150 g, 200 g), but same size (same radius), and a metre scale

Principle / Theory
The time period T of a simple pendulum of length L is given by the relation.

L
T = 2π
g

Here 'g' is the acceleration due to gravity.
It clearly indicates that,
T ∝ L

1
and T ∝
g

But the time period of a simple pendulum is independent of the mass of the bob. So, for the same value of
L and g, the time period of a simple pendulum is same for two bobs of diff erent masses.

Procedure
Clamp
Split
cork S S
Stand Thread
Table

l′
L
Hook
O h T
C 5 cm 5 cm B L=l'+h+r r G C.G. of the bob

Fig. 8.1: Simple pendulum Fig. 8.2: Eff ective length
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