Physics (school) · Part 05
Waves, sound and light
How waves carry energy, from ripples and echoes to the whole light spectrum.
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- WavesA wave carries energy from place to place without carrying matter. Transverse waves wiggle at right angles to the direction of travel. Longitudinal waves push and pull along it.
- Amplitude, wavelength and frequencyAmplitude is the wave's maximum displacement from rest. Wavelength is the distance between matching points on neighbouring waves, in metres. Frequency is the number of waves per second, in hertz (Hz).
- Wave speed equationWave speed = frequency x wavelength (v = f x lambda), measured in m/s.
- ReflectionA wave bounces off a surface. The angle of incidence equals the angle of reflection, both measured from the normal (a line at right angles to the surface).
- RefractionA wave changes speed, and usually direction, when it passes from one material into another. Light bends towards the normal when it slows down.
- Electromagnetic spectrumA family of transverse waves that all travel at the speed of light in a vacuum (300,000,000 m/s). From long to short wavelength: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma.
- SoundSound is a longitudinal wave made by vibrations. It needs a material to travel through. It moves at about 340 m/s in air, faster in liquids and solids.
- Pitch and loudnessPitch is how high or low a note sounds and depends on frequency. Loudness depends on amplitude. Humans hear about 20 Hz to 20,000 Hz.