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neurologyYou need to know

• A transverse wave has oscillations perpendicular to the direction of energy transfer.
• A longitudinal wave has oscillations parallel to the direction of energy transfer.
• Waves transfer energy from one place to another without transferring matter overall.
• The wavelength of a wave is the distance from one point on a wave to the same point on the next wave, such as crest to crest or compression to compression.
• The amplitude of a wave is the maximum displacement of a point on the wave from its rest position.
• The frequency of a wave is the number of complete waves passing a point each second, measured in hertz.
• The time period of a wave is the time taken for one complete wave to pass a point, measured in seconds.
• Compressions are regions in a longitudinal wave where particles are close together, and rarefactions are regions where particles are spread apart.
• Wave speed is calculated using `v = f \lambda`, where `v` is wave speed in metres per second, `f` is frequency in hertz, and `\lambda` is wavelength in metres.
• Frequency and time period are related by `f = \frac{1}{T}` and `T = \frac{1}{f}`, where `T` is time period in seconds.
• The electromagnetic spectrum, in order of increasing frequency and decreasing wavelength, is radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
• All electromagnetic waves are transverse waves and travel at the same speed in a vacuum, about `3.0 \times 10^8` metres per second.
• Radio waves can be produced by oscillating electrical charges in aerials and are used for broadcasting, television and communications.
• Microwaves can be produced by electronic oscillators and are used for satellite communication, mobile phones and heating food.
• Infrared radiation is emitted by warm objects and is used in heaters, thermal imaging and remote controls.
• Visible light is emitted by hot objects and some electronic devices, and it is the only part of the electromagnetic spectrum detected by the human eye.
• Ultraviolet radiation is emitted by very hot objects such as the Sun, causes tanning and sunburn, and is used in fluorescent lamps and security marking.
• X-rays and gamma rays are high-frequency ionising radiations; X-rays are used for medical imaging and gamma rays are used for sterilising equipment and treating cancer.
• Ionising radiation can remove electrons from atoms, which can damage cells, cause mutations and increase the risk of cancer.
• At a boundary between materials, light can be reflected, transmitted or absorbed; refraction happens when light changes speed as it passes from one material into another.

• Identify a wave as transverse or longitudinal by comparing the direction of particle oscillation with the direction of energy transfer.
• Label wavelength, amplitude, compression and rarefaction correctly on diagrams of transverse and longitudinal waves.
• Calculate wave speed, frequency or wavelength by selecting and rearranging `v = f \lambda` and using standard units.
• Calculate frequency or time period by selecting and rearranging `f = \frac{1}{T}` and converting units where needed.
• Place the regions of the electromagnetic spectrum in the correct order from radio waves to gamma rays, or from gamma rays to radio waves.
• Compare regions of the electromagnetic spectrum by describing their relative wavelength, frequency, typical uses and whether they are ionising.
• Explain refraction by linking a change in material to a change in the speed of light and a change in direction when the ray enters at an angle.
• Predict the effect of a colour filter by stating that it transmits a narrow range of wavelengths and absorbs most other wavelengths.