Sound Waves

PRODUCTION

Sound waves are produced by vibrating objects. Some of the source of sound are talking, shouting, beating, beating drums, blowing of flutes, shooting of a rifle, a ringing telephone, the noise from moving cars and airplanes and musical instruments.

TRANSMISSION OF SOUND WAVES

Sound travels from place to place as sound waves. Sound must have a substance to travel through i.e it does not travel through a vacuum. There is nothing in a vacuum to pass on a vibrations. Sound waves are longitudinal waves i.e the air vibrates backwards and forwards in the wave is moving.

It can travel through solids, liquids and gases. The air changes the vibration into impulses which are carried into brain for interpretation.

CHARACTERISTICS OF SOUND

A. PITCH

This depends on the frequency of the sound waves. If the frequency is increase, the pitch of the sound also increases.

B. LOUDNESS

The loudness of the sound depends on its intensity. The intensity of the sound of the wave is the rate of the flow of energy per unit area, perpendicular to the direction of the wave.

Intensity is proportional to the square of the amplitude. The greater the intensity, the louder the sound.

C. QUALITY

This is the property which enables us to distinguish the same note  played on different instruments e.g a piano and an organ, the quality of a musical notes depends on the harmonies. When a note is produced, the strongest, audible frequency heard is the fundamental. All other frequencies present ar harmonics or overtones.

FORCED VIBRATION

If tuning fork A is struck and stopped, you find that it will cause tuning fork B to vibrate, provided both forks have the same frequency. This is called forced vibration. Other form off forced vibration include:

(1) RESONANCE

Resonance is a special case of forced vibration which occurs when a system is made to vibrate at its own natural frequency as a result of forced vibrations received from another sources of the same frequency.

(11) RESONANCE IN STRINGS

stationary waves can occur on a stretched string or wire.. This is obtained by varying the driving frequency of the string.

General revision

1. A  machine of velocity ratio 5 is used to raise a load with an effort of 500N if the machine is 80% efficient determine the magnitude of the load
2. A machine of efficiency 80% is used to raise a body of mass 75Kg through a vertical height of 3m in 30s. Calculate the power output

Weekend Assignment

1. Sound wave differs from water wave………

(a)energy transfer is involve                (b) they can be refracted and reflected

(c )no transfer of the medium is involved           (d)They are longitudinal wave.

      2.    A source of sound produces waves in air if wavelength 1.65m. if the speed of sound in             air is 330m/s, the period of vibration is.

           (a) 200              (b) 0.005                      (c ) 0.5        (D) 0.02

      3.  The speed of sound traveling in various media increases in the following correct order.

         (a) Iron bar, air, water    (b) air, iron bar, water  (c) air, water, iron bar (d) water, iron bar,            air.

      4.  Why does the sound from an enclosed bell jar gradually fade away as the jar is gradually          evacuated? (a) the sound is forced out (b) the pressure within the jar is reduced (c) there

         is no more material medium     (d) the temperature is reduced.

      5.  A noise of frequency 2000Hz has a velocity of 400m/s. What is the wavelength of the           noise? (a) 0.02m       (b) 0.25m      ( c ) 0.2m      (d) 2m

Theory

1.  Define a musical note
2. Mention the three characteristics of sound and the factors on which they depend

Reading Assignment New School Physics, pgs. 332-341