Musical Instruments

(A) WIND INSTRUMENTS

Clarinets, flute, saxophone, trumpet are examples of wind musical instruments. A musical note originates from a source vibrating in a uniform manner with on or more constant frequencies music is a combination of musical notes. All wind instrument use resonating air columns to produce their sounds.  Sounds from wind instruments may  originate from (1) Air vibrating over an opening e.g. organ and flute.

(2) The vibrating lips of a brass instrument e.g. trumpet.

(3) A vibrating heel e.g. clarinet, saxophone.

Some columns are of fixed length, their resonant frequencies being altered by the opening or the closing of holes in the column e.g. clarinet, a recorder, some instruments are played by altering the length the air column e.g.  a trumpet.

(B)STRINGED INSTRUMENTS

The guitar, the sonometer and piano are examples of stringed musical instruments. These instruments may be set in vibration by a bow, or plucked with a finger e.g. a violin is bowed while a guitar is plucked. The frequency of a vibrating string depends on its length, the mass and the force that keeps the string taut. Stringed instruments vibrate as a whole and in loops  at the same time e.g. the violin. These vibrations produce both the fundamental and overtones frequencies.

(C) PERCUSSION INSTRUMENTS (drums, bell, talking drum)

Percussion instruments produce musical notes when they are struck or hit. They have rods, plates or membranes that vibrate when struck; for example, there are rods in bells, plates (bars) in xylophones and membrane in drums.

ECHOES AND THEIR APPLICATION

An echo is the repetition of sounds caused by the reflection of sound waves from a hard surface. Such as buildings, walls and cliffs are good reflector of sound.

Echoes have practical importance in the development of sonar, speed traps, prospecting for oil and determining the speed of sound. In the determination of speed of sound by echo, we use the expression

2x = V t

Where

V  = velocity of sound            x = distance between the source of sound and reflecting surface

t = total time taken

EVALUATION

1. What are beats?

2. State three applications of echo

General Revision

1. A boat is rocked by waves of speed 30m/s whose successive crests are 10m apart. Calculate the rate at which the boat receives the waves.

2. A body is projected horizontally from the top of a cliff 45m above the ground. If the body lands at a distance 30m from the foot of the cliff, calculate the speed of the projection. ( g = 10m/s² )

Reading Assignment

New School Physics Pgs 342 – 347

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