Waves

Waves transfer energy from one place to another through vibrations. The wavelength of a wave is the distance between two successive crests (length). The amplitude of a wave is the maximum displacement of a particle in the wave from its equilibrium position (length). The frequency of a wave is the number of waves that pass a point in one second (Hertz).

Transverse Waves – In transverse waves, particles oscillate perpendicularly to wave direction:

Examples of transverse waves include electromagnetic waves and water waves.

Longitudinal Waves –

In longitudinal waves, particles oscillate parallel to wave direction:

Examples of longitudinal waves include sound and ultrasound waves.

Velocity of a Wave – The velocity of a wave is given as: Velocity = Frequency x Wavelength

Reflection of Waves –

Note: wavelength stays constant before and after reflection.

Refraction of Waves –

Wavelength decreases when moving from deep to shallow water: consider V = ƒ λ, where ƒ is constant, so the decrease in velocity must coincide with a decrease in wavelength. Refraction occurs due to the change in speed of the wave as it enters a different medium.

Dispersion of Light – White light is made of all the colours of the visible spectrum. Each colour has a different wavelength/frequency and so travels at a different speed. Each colour will also therefore bend by a different amount when travelling through a different medium. Red bends the least, Violet bends the greatest.

If red light is shone through a prism, it will refract but not disperse, as it is described as monochromatic.

Sound Waves – Sound waves can also reflect, and these are called echoes. Sound travels at approximately 330m/s in air, and 1500m/s in water. The echo principle can be used in sonar equipment, for example, on boats to locate shoals of fish, by recording the time taken for the sound wave to leave the boat, reflect, and hit it again, dividing this by two and then calculating the distance. Ultrasound (i.e. sound waves above 20KHz, which the human ear cannot detect) has other practical uses:

Electromagnetic Waves – All EM waves share three properties: They all travel at 3×108 m/s They are all transverse They can all travel through a vacuum.

Uses and Dangers –