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neurologyYou need to know

• A wave is a disturbance that transfers energy from one place to another without transferring matter overall.
• In a transverse wave, the oscillations are perpendicular to the direction of energy transfer.
• In a longitudinal wave, the oscillations are parallel to the direction of energy transfer.
• Wavelength is the distance from a point on one wave to the same point on the next wave, such as crest to crest or compression to compression.
• Amplitude is the maximum displacement of a point on a wave from its rest position.
• Frequency is the number of complete waves passing a point each second, measured in hertz.
• Time period 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 closer together than normal, and rarefactions are regions where particles are further apart than normal.
• Wave speed is calculated using `v = f\lambda`, where `v` is wave speed, `f` is frequency and `\lambda` is wavelength.
• Time period and frequency are linked by `T = \frac{1}{f}` and `f = \frac{1}{T}`.
• The electromagnetic spectrum, from longest wavelength to shortest wavelength, is radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
• All electromagnetic waves are transverse waves that can travel through a vacuum at the same speed of about `3.0 \times 10^8` metres per second.
• Radio waves can be produced by oscillating charges in electrical circuits and are used for broadcasting, communications and radar.
• Microwaves can be produced by oscillating charges in electrical circuits or by special microwave sources, and are used for satellite communication, mobile phones and cooking food.
• Infrared radiation is emitted by warm objects and is used in thermal imaging, heaters, remote controls and optical fibre communication.
• Visible light is emitted by hot objects and some electronic devices, and is used for vision, photography and optical communication.
• Ultraviolet radiation can be emitted by very hot objects and special lamps, and it can cause fluorescence, sunburn and damage to skin cells.
• X-rays and gamma rays are high-frequency ionising radiations that can damage cells and DNA, increasing 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 between materials such as air, glass or water, causing the light to change direction if it enters at an angle.

• Identify transverse waves by locating crests, troughs, wavelength and amplitude, and identifying particle motion at right angles to energy transfer.
• Identify longitudinal waves by locating compressions, rarefactions and wavelength, and identifying particle motion parallel to energy transfer.
• Calculate wave speed, frequency or wavelength by rearranging and substituting into `v = f\lambda` with correct units.
• Calculate time period or frequency by using `T = \frac{1}{f}` or `f = \frac{1}{T}` with correct units.
• Arrange the electromagnetic spectrum in order of wavelength, frequency or energy, recognising that frequency and energy increase as wavelength decreases.
• Compare regions of the electromagnetic spectrum by linking their wavelength, frequency, production, properties and common uses.
• Explain the risk from ionising electromagnetic radiation by linking high photon energy to cell or DNA damage.
• Explain reflection, transmission and absorption at a boundary by describing what happens to the incident light energy.
• Explain refraction by linking a change in material to a change in light speed and, when the ray enters at an angle, a change in direction.
• Predict the colour of light transmitted by a filter by stating that filters transmit only a narrow range of wavelengths and absorb the others.