Page 52 - Physics - XI

Graph: Plot a graph between L and T taking L along X-axis and T along Y-axis. The graph would be a
2
2
straight line as shown in Fig. 7.6
Y

5.00

4.75
4.50
T 2 (s 2 ) 4.25

4.00 A P Scale used:
3.75 X-axis : 1 cm = ... cm
Y-axis : 1 cm = ... s
2
3.50 B X
70 80 90 100 110 120 130
L (cm)

Fig. 7.6: Graph between L and T 2

Calculations

To fi nd the length of second's pendulum: The time period of second's pendulum is 2 seconds. If T = 2s,
T = 4s , corresponding to 4.00 s and on Y-axis (Fig. 7.6), draw a horizontal line AP which meets the graph
2
2
at P. Draw a vertical line through P which meets at B on X-axis. Read L according to point B on X-axis
which is the length of the second's pendulum.

Result
1. The graph between L and T is a straight line.
2
2. From the graph, the length of the second's pendulum is ..... cm.
Precautions

1. The point of suspension should be fi xed in a rigid support.
2. The thread should be inextensible and strong.

3. The amplitude of the pendulum should be small so that sin θ ≈ θ.
4. The bob should move along a straight line and it should not have any spin during the vibration.

5. Length of the pendulum should include the length of the hook and the radius of the bob.
6. The experiment should be performed at a place where air disturbance should be minimum, even the fan
should be switched off .

7. Start recording time after pendulum has made a few vibrations.
8. Lower faces of the split cork should lie in the same horizontal plane.

9. Splitting of the corks should be perpendicular to the plane of the vibration of the pendulum.

Sources of Error

1. The thread may not be inextensible.
2. The suspension support may not be rigid.

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