Sonometer

- A sonometer
- A set of tuning forks of known frequency
- 0.5kg weight hanger
- Some 0.5kg slotted weights
- Rubber pad
- Paper rider

- Place the sonometer on the table.
- Make sure that the pulley is frictionless. If you feel any friction, oil them.
- Stretch the wire by placing a suitable maximum load on the weight hanger.
- Move the wooden bridges outward, so that the length of wire between the bridges is maximum.
- Take a tuning fork of known frequency. Make it vibrate by strike its prong with a rubber pad. Bring it near the ear.
- Pluck the sonometer wire and leave it to vibrate.
- Compare the sounds produced by tuning fork and sonometer wire. (Sound which has low pitch has less frequency).
- Gently adjust the bridges for decreasing the length of wire, till the two sounds appear alike.
- Put an inverted V shaped paper rider on the middle of the wire.
- Vibrate the tuning fork and touch the lower end of its handle with sonometer board. The wire vibrates due to resonance and the paper rider falls.
- Measure the length of wire between the bridges using a meter scale. It is the resonant length and record it in the ‘length decreasing’ column.
- Now, bring the bridges closer and then slowly increase the length of the wire till the paper rider falls.
- Measure the length of wire and record it in ‘length increasing’ column.
- Repeat the above steps with tuning forks of other frequencies, and find resonant length each time.

- Select a tuning fork of known frequency
- Set the load in the weight hanger as maximum.
- Repeat the steps in the previous section to find out the resonant length.
- Now, remove 0.5kg weight from the weight hanger and find resonant length with same tuning fork.
- Repeat the experiment by removing slotted weights one by one in equal steps of 0.5kg.
- Record the observations each time.

- Select the environment from the drop down list.
- Select the material of the wire from the drop down list.
- Select the diameter of the wire using the slider.
- Select the weight of the slotted weights using the slider.
- Select the frequency of the tuning fork using the slider.
- Click on the ‘Hit tuning fork’ button to start/stop the vibration of tuning fork and touch it with the sonometer board.
- Change the position of bridge A using the slider.
- Change the position of bridge B using the slider.
- Click on the ‘Place the paper rider’ button to place the paper rider back.
- To redo the experiment, click on the ‘Reset’ button.

Constant tension on the wire, T= .........kg

Sl No. | Frequency of tuning fork used, f (Hz) | Resonant length of wire | 1/ (cm |
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Length increasing l_{1}(cm) |
Length decrasing l |
Mean l = (l_{1} +l_{2}) / 2 |
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Sl No. | Load, M (kg) | Tension, T=Mg (N) | Resonant length of wire | l (cm |
l (cm |
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Length increasing l_{1}(cm) |
Length decrasing l_{2} (cm) |
Mean l = (l_{1} +l_{2}) / 2 |
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Mean, l^{2} / T =.................. cm^{2} / N

- Find mean resonant length, l
- Calculate 1/l in each case.
- Plot a graph between frequency and reciprocal of length, taking frequency along X axis and reciprocal length along Y axis.

- Find square of resonant length (l
^{2}) each time. - Calculate corresponding l
^{2}/T value. - Plot a graph between square of length and tension, taking tension along X axis and square of length along Y axis.

The frequency V/s reciprocal of length graph is a straight line, which indicates that, frequency is inversely proportional to resonant length.

From the tabular column, it is found that; l^{2}/T is a constant. The graph between square of length and tension is a straight line, which shows that tension is directly proportional to square of resonant length.