Page 42 - Physics - XII

5. Now, switch on the A.C. supply and adjust the length of the vibrating portion of the sonometer wire
by sliding one of the wedges until the wire begins to vibrate. Again make small adjustments till the
amplitude of vibrating wire between the two bridges is maximum.

6. Note down the length of the vibrating wire (when its amplitude is maximum) between the two wedges
A and B and the value of the tension T = Mg (where M = weight of hanger + slotted weights on it).
Length AB of wire gives resonant length l.
7. Bring the two wedges closer and then adjust the length for maximum amplitude by increasing it.
Now, measure the length AB and tension T.
8. Now, make the two wedges apart from each other and go on decreasing the length of the wire AB

between the two wedges and adjust the length for maximum amplitude by decreasing it. Measure the
length AB between the edges of the two wedges.
9. Ensure that both lengths (increasing or decreasing) will be taken for the same tension in the wire.
10. Now, increase the tension (load) in the step of 0.5 kg weight and repeat the steps 6, 7, and 8 and record
the maximum amplitude in wire AB.

11. Take four sets of observations in all for diff erent loads.
12. Switch off the A.C. supply to the electromagnet and remove it.
13. Take about 100 cm of the sonometer wire and fi nd out its mass by a sensitive physical balance and
record it.

Observations
1. Length of the sonometer wire = L = _____ cm = _____ m
2. Mass of this length L of the sonometer wire = W = _____ g = _____ kg

3. Mass per unit length of the sonometer wire = m = W/L = _____ g/cm = _____ kg/m
4. Mass of the hanger = _____ g = _____ kg
5. Value of acceleration due to gravity = g = _____ m/s .
2
Table for resonant length of the wire
S. Load Tension Resonant length of the sonometer wire Frequency
No. (including T = Mg Length Length Mean length 1 T
mass of the (N) increasing decreasing l l n == l 2 m
hanger M) l l l 1 2 2
2
1
(kg) (cm) (cm) (cm) (Hz)
1.
2.
3.
4.

Mean frequency n = _____ Hz

Calculations

Using formula n = 1 T , calculate the value of n for each set of observation and fi nd the mean
value of n. 2l m

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