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:

  1. Transverse waves
  2. 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.

Sound waves are examples of longitudinal waves. All longitudinal waves show areas of compression and rarefaction which help them spread easily.

Describing waves

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.

Common misconceptions

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:

Wave speed

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:

  1. The speed of a wave
  2. The frequency of a wave
  3. 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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