AQA A-Level Physics/Longitudinal and transverse waves

Longitudinal and transverse waves are the two main classifications/types of waves.

Transverse Waves

Transverse waves are characterised by the fact that the direction of energy transfer is perpendicular to the direction of wave oscillation and particle displacement.

Examples of Transverse waves include the whole EM Spectrum, secondary earthquake waves, and waves formed along a string.

It is also important to note that all EM waves travel at the same speed in a vacuum, that being 3.00*10^8ms^-1

Most transverse waves cannot travel through liquids. While oceanic waves themselves are transverse, these waves instead propagate through the surface tension of the ocean.

Light and EM waves are also 'self propogating', meaning they sustain themselves using their own magnetic field, and can therefore travel through liquids.

This self-propogation concept is not assessed in any of the Physics A-Level, however it may help with your understanding of transverse waves.

Polarisation of Transverse Waves

Transverse waves can also be polarised. Polarisation is the act of restricting the vibration of a transverse wave to one vertical plane / direction. This can, in many cases where a pulse of light will consist of many different individual waves oscillating in different directions, reduce the amount of perceived light that would pass through the polarising filter.

Therefore, polarising filters are used in various everyday applications, such as;

• Sunglasses, to reduce the impact of sun on the vision of the user.
• Camera Lenses, to reduce glare and its impact on a picture taken.
• Antennas, Waves must be aligned with Antenna receivers to ensure a good reception signal.

This feature of polarisation is exclusive to Transverse Waves. Therefore, in scientific applications, polarising filters can be used to easily and effectively determine the type of wave when this is not a known quantity.

Longitudinal waves

Longitudinal waves are characterised by the fact that the direction of energy transfer is parallel to the direction of wave oscillation and particle displacement.

Examples of Longitudinal waves include sound waves, primary earthquake waves, and ultrasound waves.

Longitudinal waves cannot be polarised.