Waves 🌊

• When a wave passes through a material, the final displacement of the waves is zero.
• Waves do not move particles but move energy from one place to another.
• The frequency of a wave is how many waves are produced each second or how many passes a point in a second.
• High frequency means more waves per second.
• The unit for frequency is the Hertz, Hz, which means per second.
• The period, T, is the time it takes one wave to pass a point, measured in seconds s.
• The frequency, f, is the number of waves per second, measured in Hertz, Hz.
• The midpoint is where the material or field would be without the wave.
• The crest is the maximum displacement of a wave above its midpoint, measured in metre m.
• The trough is the maximum displacement of a wave below its midpoint, measured in metre m.
• The wavelength, λ, is the distance between two exact same points on a wave, such as crest to crest, trough to trough, measured in metre m.
• Infrared radiation allows us to see.
• Infrared radiation is detected by a photodiode, a phototransistor, a thermistor, and a LDR.
• Gamma radiation is used in medical tracers.
• Infrared radiation is emitted by very hot objects and lamps.
• Gamma radiation is produced by nuclear decay and cosmic rays.
• X-rays are detected by a photographic film and a photodiode.
• Microwave radiation is used in mobile phone signals and antennae.
• Gamma radiation is detected by a photodiode and a Geiger-Muller tube.
• Ultraviolet radiation is emitted by very hot objects and electrical discharges/sparks.
• Microwave radiation is emitted by electrical circuits and starlight.
• X-rays are produced by man-made sources and some natural rocks.
• Ultraviolet radiation is used in detecting counterfeit bank notes, setting dental fillings, and sterilising medical instruments.
• Ultraviolet radiation is detected by a photodiode, a phototransistor, and fluorescent materials.
• X-rays are used in airport security, medical examinations, and non-destructive testing.
• The amplitude, A, is the displacement from the midpoint to either a crest or trough.
• Longitudinal waves are waves where the particles move at right angles to the direction the wave is travelling.
• In longitudinal waves, the particles vibrate in the same direction as the wave is travelling.
• For longitudinal waves, crests and troughs are replaced with compressions, where the particles are squeezed together, and rarefactions, where the particles are stretched apart.
• A wavelength is the distance between two compressions or the distance between two rarefactions.
• Sound is an example of longitudinal waves.
• Longitudinal waves require particles to travel through.
• Transverse waves do not require particles to travel through.
• The time taken for one wave is called the period, T.
• Frequency is measured in Hertz, Hz, which is the same as per second.
• Wavespeed is how fast the wave travels and is measured in metres per second, m s‑1.
• When waves go through a gap in a barrier, they bend at the edges, this effect is known as diffraction.
• As the wavelength becomes shorter, the frequency increases.
• Electromagnetic waves of higher frequency have greater energy and are potentially more dangerous.
• The narrower the gap, the greater is the amount of bending of the waves.