i. law of length
, ii. law of tension (faT),
iii. law of mass
Apparatus:
Sonometer, pieces of wire of different diameters, wedges, slotted weight set. L – shaped permanent magnet, bulb 10 watt, power amplifier, audio frequency single generator.
Procedure of law length:
Place Sonometer on the table with pulley m the edge side. Stretch a thin steel wire (34. 36 SWG) with a load of 1.0 kg. Fix the U shaped magnet with plasticine on the sonometer at the mid-point so that the stretched wire passes between its poles. Adjust the two wedges so that the length of wire between them is about 70 to 80 cm. Record the length I. put a paper rideron it in its middles.
Connect the output terminals of power amplifier at the two ends of the stretched wire with a bulb in series. Set the volume of amplifier. Connect the input terminals of power amplifier to the audio frequency signal generator. Connect both with main A.C. Slowly increase the frequency of the signal so that rider may fall off. Note the frequency.
Repeat this procedure for different lengths. Plot a frequency against 1/1 graph. This graph should be a straight line.
Procedure of law of tension:
Set the frequency of the signal generator to 10 Hz. Decrease the mass to 0.5 kg so that the tension in the wire is now 4.7 N. Note the rule. Slowly increase the frequency of the signal generator till rides off. Note the frequency. Increase the mass. Replace the rider on the wire and increase the frequency of the signal generator further till resonance occurs and rider falls off. Note the tension and frequency. Repeat for several tension (T) against different frequencies.
| No. of Obs | Mass stretched | Tension(T) | Frequency of Resonance | F2 | F2 /T |
| 1 2 3 |
Procedure of law of mass:
Same set is used for this experiment only by changing the wire of different diameter keeping distance between the wedges sa
Precaution:
1. While changing the position of the movable bridge adjust the paper rider always in the middle of the wire.
2. The wire must be straight and without kinks having uniform area of cross section.
3. Using bridges of sharp edges.
VIVA VOCE
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 monochrod?
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.
Q-7 why does the Sonometer consists of a hollow wooden box?
A- The Sonometer consists of a hollow box because loudness of sound ernitted by the wire or any other vibrating source placed in contact with it is increased by the hollowness of the wooden box.
Q-8 what are beats?
A- The rise and fall in the loudness of sound of two vibrating bodies of nearly equal frequencies are called beats.
Q-9 Are sound waves transverse waves?
A-No, sound waves are longitudinal waves.
Q-10 A stretched string of length ‘I’ vibrates in a single loop what is the wavelength of the stationary waves produced?
A- The distance between two consecutive nodes is given by =1 or 2-21
Q-11 what is law of length?
A- According to law of length, “The frequency of vibration of stretched string is inversely proportional to the length of the string.”
i.e. Or
Q-13 what is law of mass?
A-According to law of mass, “The frequency of vibration of stretched string is inversely proportional to the square root of the mass per unit length of string.” i.e. or constant”
i.e. or = constant
