TOPIC HINTS:
- Introduction to waves
- Behaviour of waves
- Propagation of waves
- Sound waves
- Musical sound
- Electromagnetic spectrum
- Application of electromagnetic spectrum
Wave is a periodical disturbance that transfers energy from one point to another.
TYPES OF WAVES
There are two broad (main) categories of waves.
1. Electromagnetic waves
2. Mechanical waves
ELECTROMAGNETIC WAVES
Are disturbances made up of electric and magnetic fields
OR
Are waves that are produced by electromagnetic vibrations.
Electromagnetic waves does not require material medium to transfer energy.
Examples of electromagnetic waves are Radio waves, light waves.
MECHANICAL WAVES
Are waves which transfer energy from one place to another through a medium.
OR
Are waves which travel through materials (medium).
Examples of Mechanical waves are water waves, sound waves, vibrating string, seismic waves.
Energy is transferred due to particle to particle wave action.
TYPES OF MECHANICAL WAVES
Mechanical energy can further be sub divided into two categories.
1. Transverse waves
2. Longitudinal waves
TRANSVERSE WAVES
Are waves which travel perpendicular to the direction of the vibrations.
OR
Are waves that make the particles of the medium vibrate in a direction perpendicular to the direction of the movement of wave.
Examples of transverse waves are water
waves, light waves, radio waves and secondary (S-waves) waves.
LONGITUDINAL WAVES
Are waves which travel in a direction parallel to the vibrations.
OR
Are waves that the particles of the material medium vibrate in a direction parallel to the direction of the wave motion.
An example of longitudinal waves is sound waves and Primary (P-waves) seismic waves.
Note:
Water waves can be longitudinal or transverse, depending on the way the disturbance was made.
Eg. An object dropped into water, longitudinal waves are produced.
TERMS USED IN WAVES
i) PERIOD
Is the duration of one cycle of a wave. The time taken for the wave to complete cycle, it is represented by letter. The SI –unit for period is the second (s)
ii) AMPLITUDE
Is the maximum displacement of the wave from the equilibrium position. It is represented by the letter, A. The SI – unit for Amplitude is the metre (m)
iii) CREST AND TROUGH
Crest – Is the point of maximum positive displacement of the wave from equilibrium position.
Trough – Is the point of maximum negative displacement of the wave from equilibrium position.
iv) WAVELENGTH
Is the distance between two successive or adjacent crests or troughs.
The distance that wave travels one cycle. It is represented by Greek letter lambda (l).
The SI –unit of wavelength is metre (m)
v) FREQUENCY
Is the measurement of a wave cycles per unit time.
OR
Is the number of wave cycles per second. It is represented by a letter f
f = 1/T
The SI – unit of frequency is Herts (Hz) or per second (S-1)
1Hz = 1 S-1
vi) WAVE VELOCITY
Is the speed at which the wave moves through a medium.
OR
Is the displacement of the wave per unit time.
OR
Is the wavelength per unit time taken to complete one cycle.
The SI-Unit wave velocity is metre per second (m/s)
RELATION SHIP BETWEEN FREQUENCY, VELOCITY AND WAVELENGTH
From;
VELOCITY = DISPLACEMENT
TIME
Velocity = wavelength
Period
V = l/T
But ¦ = 1/T, Then T = 1/f
V = l/T
V = (1/T)l
V = ¦l
Example 1
The graph below shows the displacement of a wave with time.
Determine the Amplitude, period and frequency of wave.
Solution
The amplitude of the wave = 0.5m
The period of the wave = 0.2 seconds.
The frequency = _1_
Period
¦ = 1/T
= 1/0.2
= 5 Hz.
\The frequency of the wave = 5 Hz.
Example 2
Find the wavelength of sound waves of velocity 340m/s when the frequency is 1000 Hz (1k Hz).
Solution
Data given
Velocity (v) = 340 m/s
Frequency (¦) = 1000Hz
Wavelength (l) = ?
340 = 1000l
1000 1000
l = 0.34m.
\The wavelength of sound waves = 0.34m.
CLASS ACTIVTY
1. With examples distinguish
i. Electromagnetic and mechanical waves
ii. Transverse and longitudinal waves
2. Describe how can water waves be longitudinal waves?
3. With the aid of illustration describe the terms period, amplitude, wavelength, crest, trough and frequency as used in propagation of waves.
4. With the aid of illustrations described the propagation of waves.