Apparatus:
Electrically maintained tuning fork, stout cotton thread, a light scale pan, weight box.
Rheostat .
Observations:
Mass of 1 meter long thread = m =……………………. gms
Mass of I cm thread = m= /100 =……….cms /gms
Mass of scale pan =m1 =…….cms/gms
| No. of Obs. | No of loops ‘n’ | Distance between extreme nodes ‘d’ cm | Length of scale loop L=d/ncm | Mass of pan and mass added M = m1 + m2 cm | Tension “T’ T=mgDynes | F4requency of vibration segment f=(1/20) /(T/m) |
| 1 2 3 |
By arrangement (1) Longitudinal mode
(i) Frequency of A.C. mains =1/2 Frequency of vibrating segment = c /sec .
(ii) Frequency of tuning fork f’1’ =2 x frequency of vibrating = c /sec
(1) Frequency of A.C. mains
(2) Transverse mode
(1) Frequency of A.C. mains =1/2 Frequency of vibrating segment = c /sec .
(i) Frequency of tuning fork =2 x frequency of vibrating = c /sec
Procedure:
An electrically driven tuning fork mounted on a heavy stand having an electromagnet fitted between its prongs with make and break circuit at one prong of the fork. Connect the rheostat and a switch to the secondary coil of the step down transformer in order to keep the current passing through the electromagnet in safe conditions and that the prongs of the fork vibrate properly. While the primary coil of the transformer is connected to the A.C. main.take one end of a stout cotton thread to the hook of the prong of the tuning fork. The other end of the cotton thread passing over the frictionless pulley which in turn attached to the light scale pan of the known mass.
The tuning fork will excite, when the current passed through the circuit. Place small suitable weight in the pan so that it can vibrate in one loop under forced vibration of the tuning fork. Changing the weights one after the other, till, the string will vibrate in one loop with maximum amplitude.
Note the tension Tie. weight of the pan weight added and the length ‘T’ of the string Reducing the tension to %, 1/9 and so on of its original value and the string will made to vibrate one, two three…. So on, loops.
Note the distance between two extreme nodes and find length I of one loop divided by number of loops produced. The mass per unit length can be determined as ‘m’. Calculate the frequency of the vibrating segment of the thread using the relation.
It should be noted that in arrangement (1) i.e. in longitudinal mode, the prong complete one vibration, the string completes 1/2 vibration only. While in arrangement. (11) i.e. transverse mode the string complete one vibration, the string also completes one vibration ie. both have same frequency.
Precautions:
1. Pulley should be oiled to reduce friction.
2. The thread should thin and of uniform diameter to get loops of equal length.
3. The scale pan should be light and weight added should be small.
4. The thread should be horizontal and along the mean position of the prong.
5. Loops formed should be well defined.
VIVA VOICE
Q-1 what is a Sonometer?
A– It is an instrument consists of a long hollow wooden sounding box over which one wire can be stretched.
Q-2 Why is the Sonometer also called monometer or monochord?
A- The Sonometer is also called monometer because it consists of a single wire.
Q-3 what kind of waves are produced along the wire of Sonometer?
A-Transverse stationary waves are produced along the wire of Sonometer.
Q-4 what types of vibrations are set up in the wire of the Sonometer?
A- Forced vibrations are set up in the wire of the Sonometer.
Q-5 why does he paper rider fly off at resonant length of the wire?
A- At resonant length, nodes are formed at the ends of the length and an anti-node is formed in the other middle. Since the amplitude of vibration at the anti-node is maximum, as paper rider is placed at the midpoint, so it flies off.
Q-6 what is the function of monochord?
A- Monochord is an apparatus which is used to find the unknown frequency of tuning fork.
