Types of wave SA - CCEA

• To understand the difference between transverse and longitudinal waves.

• To describe in terms of particle movement, how waves transfer energy from one place to another.

• To identify the different parts of a wave.

Waves transfer energy from one place to another through vibrations
(oscillations.)

The direction of these oscillations is the difference between longitudinal and transverse waves.

A longitudinal wave is one in which the vibrations of the particles are parallel to the direction in which the wave is travelling.

In the diagram, the compression moved from left to right and energy is transferred from left to right.

The movement of the coils of the slinky and the energy are parallel.

However, none of the particles are transported along a longitudinal wave.

Instead, they move backwards and forwards as the wave is transmitted through the medium.

Examples of longitudinal waves include:

• Sound waves.

• Ultrasound waves.

One way of remembering examples of longitudinal waves is to emphasise the O in lOngitudinal and sOund and ultrasOund.

A transverse wave is one in which the vibrations of the particles are perpendicular (at right angles) to the direction in which the wave is travelling.

How to demonstrate transverse waves

Transverse waves are often demonstrated by moving a rope rapidly up and down.

In the slideshow, the rope moves up and down, producing peaks and troughs.

Energy is transferred from left to right at right angles to the hand movement.

However, none of the particles are transported along a transverse wave.

Examples of transverse waves include:

• Vibrations in a guitar string.

• Electromagnetic waves – eg light waves, microwaves, radio waves, x-rays.

• Water waves.

Key fact

All waves transfer energy from one place to another, but they do not transfer matter.

Some important terms:

• Rest position (equilibrium position) - the undisturbed position of particles or fields when they are not vibrating.

• Displacement - the distance that a certain point in the medium has moved from its rest position.

• Peak - the highest point above the rest position.

• Trough - the lowest point below the rest position.

• Amplitude - the maximum displacement of a point of a wave from its rest position.

• Wavelength λ – distance from one point on a wave to the next identical point. Wavelength is measured in m.

• Time period T - the time taken for a full vibration of the wave, usually measured from peak to peak, or trough to trough. Period is a time and so is measured in s. A period of 2 s means that the time for one complete vibration is 2 s or that the time taken for one complete wave to pass a point is 2 s.

• Frequency f - the number of waves passing a point each second, or the number of vibrations each second. Frequency is measured in hertz, Hz. A frequency of 50 Hz means there are 50 vibrations every second, or that 50 waves pass a point in one second.