Page 51 - Physics - XI

8. When amplitude of the vibration of the bob becomes small, start the stopwatch when the bob just
crosses its mean position O (say from left to right) and count it as zero vibration. When the bob again
passes through O in the same direction (from left to right), i.e., O to B, B to C, and back to O one

vibration is just completed.
9. In this way count 20 vibrations. When 20 vibration is just completed, stop the stopwatch. Note the
th
reading of the stopwatch. This gives the time taken for 20 vibrations. Repeat this observation by taking
the time for 20 vibrations once again at the same eff ective length of the pendulum. Take the mean of
these two readings.
10. Now, decrease the eff ective length of the pendulum 10 cm by pulling the thread up. Now, repeat the

steps 7, 8, and 9 and again record the time for 20 vibrations for this length. In the same manner, take
5 more observations for the diff erent lengths, each time decreasing the length by 10 cm. Note all
observations in the observation table.

Observations
Vernier constant of the Vernier Callipers = (V.C.) = ______ cm
Zero error of Vernier Callipers (e)

(i) = ______ cm (ii) = ______ cm (iii) = ______ cm
Mean zero error = e = ______ cm.

Mean zero correction= ( – e) = ______ cm
Observed diameter of the bob
(i) = ______ cm (ii) = ______ cm (iii) = ______ cm

Mean observed diameter of the bob = (d ) = ______ cm
0
Mean corrected diameter= d = d + (– e) = ______ cm
0
d
Mean radius of the bob = r = = ______ cm
2
Standard value of g = 980 cm/s 2

Least Count of the stopwatch = ______ sec.

Table for calculation of L and T 2

S. Length from top of Eff ective Time for 20 vibrations t(s)
No. the bob to the point of length Time period T 2 L/T 2
suspension = l' L = l' + h + r (i) (ii) Mean T = t/20
2
2
(cm) (s) (s) t(s) (s) (s ) (cm/s )
1. 130.0
2. 120.0
3. 110.0

4. 100.0
5. 90.0
6. 80.0

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