Waves: Production and Propagation

WAVES

A wave is a disturbance which travels through a medium transferring energy from one point to another without causing any permanent displacement of the medium

A wave motion is process of transferring a disturbance from one point to another without any transfer of particles of the medium.

Types of waves

Waves are broadly classified into two types

1. Based on the medium of propagation: mechanical wave and electromagnetic wave
2. Based on the comparison of the wave direction with the direction of vibration of the particle: transverse wave and longitudinal wave

Production and Propagation of waves: Based on the medium of propagation

• Production and propagation of mechanical waves

A mechanical wave is the wave that requires material medium for its mode of propagation (or for it to transfer energy away from the source). Examples are waves traveling through springs, water waves, and sound waves

• Production and propagation of electromagnetic waves

Electromagnetic waves are waves that do not need material medium for its mode of propagation (or for it to transfer energy away from the source). Examples are radio waves, visible light, ultra-violet rays, x-rays, gamma rays. Electromagnetic waves travels at the speed of light (3.0×10⁸m).

A wave which travels along a medium transferring energy from one part of the medium to another is called a progressive wave. The progressive wave can be divided into transverse and longitudinal waves

A standing or stationary wave: this is formed when two waves travelling in the opposite direction meets or by superimposition of incident wave and its reflection. The amplitude of the standing wave varies along the wave.

Production and Propagation of waves: Based on the comparison of the wave direction with the direction of vibration of the particle

1. Transverse waves

A transverse wave is a wave in which travel perpendicularly to the direction of the vibrations producing the waves.

• Longitudinal wave

Longitudinal waves are waves which travel in a direction parallel to the vibrations of the medium.

TERMS USED IN DESCRIBING WAVES

1. Phase – particles which are at the same vertical direction from their positions of rest and are moving in the same direction are said to be in phase.
2. Cycle – is a complete to-and-fro movement or oscillation of a vibrating particle
3. The amplitude (A) – is the maximum displacement of a particle from its rest or mean position. It is measured in meter (m).
4. The period (T) – is the time required for a particle to perform one complete cycle or oscillation
5. Frequency (f) – is the number of complete cycles made in one seconds.  It is measured in Hertz (Hz)
6. Wavelength (λ) – is the distance covered by the waves after one complete oscillation. For transverse waves, it is the distance between successive crests or troughs while for longitudinal wave, it is the distance between successive compressions or rarefactions. It is measured in meter (m).
7. Wave-velocity (v) is the distance traveled by the waves in one second.  The S.I unit is m/s

Worked examples on Waves

CLASSWORK 8

1. What is wave?
2. Elias radio station broadcasts at a frequency of 21MHz. If the speed of light in the air 3×10⁸ms^-1, calculate the wavelength of the broadcast. 
3. Define stationary wave

ASSIGNMENT 8

SECTION A

1. An electromagnetic radiation has a speed of 3×10⁸ms^-1 and a frequency of 10⁶Hz, calculate its wavelength (a) 3.3×10³m (b) 3.0×10²m (c) 3.0×10^-2m (d) 3.3×10⁸m (e) 3.3×10^-3m
2. Which of the following is not a mechanical wave (a) wave propagated in stretched string (b) waves in a closed pipe (c) radio waves (d) water waves (e) sound waves
3. The maximum displacement of particles of wave from their equilibrium positions is called (a) wave velocity (b) period (c) amplitude (d) wavelength (e) frequency