Waves

Waves

Waves transfer energy without transferring matter. This is shown in the sea, where buoys stay still despite waves passing by them – the waves move, but not the particles

Wavelength

The distance between the same points on two consecutive waves

Amplitude

The distance from equilibrium line to the maximum displacement (crest or trough)

Frequency

The number of waves that pass a single point per second

Period

The time taken for a whole wave to completely pass a single point

Wavefront

The plane in which the wave travels (i.e. the direction of the wave)

velocity

frequency × wavelength = v = fλ

Wave speed

Wave speed (metre/second, m/s) = frequency (hertz, Hz) × wavelength (metre, m)

Relationships

Increase frequency, velocity increases; Wavelength increases, velocity increases; Period is inversely proportional to frequency; Smaller period, higher frequency, greater velocity

Transverse waves

Has peaks and troughs; Vibrations are at right angles to the direction of travel e.g. Light, seismic S waves, water waves

Longitudinal waves

Has compressions and rarefactions; Vibrations are in the same direction as the direction of travel e.g. Sound waves, seismic P waves

Refraction

If passing into a more optically denser medium the wave refracts at the boundary, changes direction bending towards the normal, speed decreases, wavelength decreases, frequency stays constant

Reflection

Waves reflect off a flat surface; Angle of incidence = angle of reflection; Light reflects if opaque object is not absorbed

Transmission

Waves pass through transparent material; More transparent more light passes through

Absorption

Light absorbed by electrons and not reemitted if matches energy levels; Absorbed frequencies converted to heat over time

Wavelength effects

Substances may absorb, transmit, refract or reflect waves depending on wavelength e.g. glass transmits visible light, reflects UV

Ultrasound

Sound wave >20 000Hz frequency used in sonar, foetal scanning

Infrasound

Sound wave <20Hz frequency used to explore Earth's core