Properties of waves
In this guide, we are going to concentrate on two important types of waves: transverse and longitudinal, and the ways of describing them using the properties of waves.
Types of waves
Though several types of waves exist in physics, there is a special category of waves known as mechanical waves which are waves formed by a disturbance such as a vibrating object.
There are two types of mechanical waves:
- Transverse waves
- Longitudinal waves
Transverse and longitudinal waves
Transverse waves are mechanical waves in which the vibrations are at right angles to the direction in which the wave is travelling.
Here are some examples of transverse waves:
- Light waves are transverse waves.
- All kinds of electromagnetic waves (such as radio waves, microwaves, X-rays etc.) are transverse waves.
- Even the waves of water are transverse waves!
Longitudinal waves are mechanical waves where the direction of the waves is forwards and backwards, along the direction in which the wave is travelling.
Having studied transverse and longitudinal waves, we are now going to focus on some important terms that can be used to describe waves:
Wavelength and amplitude
The wavelength of a wave is the distance from one crest of the wave to the next (or the distance from one trough of the wave to the next). As wavelength is distance, it is measured in meters (m). (You may have noticed the symbol used as the symbol of wavelength. This is the Greek letter known as ‘lambda’)
The amplitude A of a wave is the maximum height of a crest of a wave. Like wavelength, amplitude is also measured in meters (m). For sound, the greater its amplitude, the louder it is.
Please note that the amplitude is measured from the undisturbed level, to the height of the crest.
Candidates often make mistakes and consider the amplitude to be the distance from the trough of a wave, up to its crest! Be careful!
Frequency and period
The frequency f of a wave is the number of waves produced each second. Frequency is also defined as the number of crests produced per second. Frequency is measured in hertz (Hz). One Hertz is one complete wave; a wave with a frequency of 10Hz means that there are 10 waves produced per second.
The period T of a wave is the time taken for one complete wave to pass a point. A period of a wave is measured in seconds (s).
Frequency and periods are related to each other; waves with shorter periods tend to have higher frequencies.
This brings us to the equations that relate frequency and period of waves:
The speed of a wave is the rate at which the crest or any point on the wave covers a particular distance in a second.
Speed, frequency and wavelength
We can write an equation that relates:
- The speed of a wave
- The frequency of a wave
- The wavelength of a wave
This equation is also known as the wave equation:
Finally, here are some of the properties of waves:
Reflection of waves
Waves are reflected when they strike a surface just as light is reflected all around. Here the angle that a wave makes against the normal (at 900) is the angle of incidence i. The angle that a wave makes while it is being reflected is the angle of reflection r. The law of reflection states that the ‘angle of incidence = angle of reflection’ which is absolutely true when it comes to all types of waves (May it be transverse or longitudinal)
Refraction of waves
Refraction occurs when the speed of light changes. The effect of refraction can also be observed in waves. The reason why refraction occurs in waves is because of the changes in wave speed due to a change in material.
Note: Waves of water tend to travel more slowly in shallow water and faster in deep.
Diffraction of waves
When a wave of water passes through a gap in a barrier, an interesting natural phenomenon can be observed:
When ripples of water pass through a gap in a barrier, they spread out into the space beyond. This phenomenon is called as diffraction.
Note: The effect of diffraction is the largest when the gap between the barrier and the wavelength of the ripples is equal.
PHET Simulation on Properties of waves
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