Page 89 - Physics - XI

5. Take the bob along the metre scale 5 cm away from the rest position (mean position) of the bob and
release it. The bob starts oscillating about the mean position O and you will observe that its amplitude
decreases as the time passes [Fig. 7.1 (a)].

6. Take the bob to its mean position O (stop position). Find out the least count of the stopwatch.
7. Again take the bob along the metre scale 5 cm away from the rest position O and release it so that it
oscillates in the same vertical plane.

8. Watch the moment of the bob when it comes to the extreme right position, start the stopwatch and also
note the position of the bob on the metre scale and record this time as zero.
9. Keep your eye on the movement of the bob continuously and observe the amplitude of the bob and
record time simultaneously after every alternate oscillation, i.e. 0, 2, 4, 6, ______ oscillations till the

amplitude decays to about 1 cm.
10. Take 10 observations.
11. Note all the observations in the table.

Observations
Mass of the bob by a physical balance = ______ g = ______ × 10 kg
–3
Least count of the stopwatch = ______ s

Eff ective length of the pendulum = l = ______ cm = ______ m

Force constant k = mg = ______ Nm –1
l

(Take the value of g = 9.8 m s )
–2

Table for the dissipation of energy

S. No. Amplitude A (cm) A (cm ) Time t (s)
2
2
1.
2.
3.
4.

5.
6.
7.
8.
9.
10.

Graph

Plot a graph between amplitude square, i.e. A and time (t), taking t along X-axis and A along Y-axis. The
2
2
graph is shown in Fig. 7.2.

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