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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 particle vibrations are perpendicular to the direction of energy transfer.
• In a longitudinal wave, the particle vibrations are parallel to the direction of energy transfer.
• Wavelength 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.
• Amplitude is the maximum displacement of a particle from its rest position.
• Frequency is the number of waves passing a point each second and is measured in hertz, Hz.
• Time period is the time taken for one complete wave to pass a point, and frequency and time period are linked by `f = 1/T`.
• Wave speed, frequency and wavelength are linked by the equation `v = f\lambda`.
• Longitudinal sound waves travel through substances by compressions and rarefactions of particles in the medium.
• Humans can normally hear sound frequencies from about 20 Hz to 20,000 Hz, and this range often reduces with age and can be affected by lifestyle factors such as exposure to loud noise.
• Waves travel at different speeds in different substances because particles and fields interact differently in different media.
• Ultrasound, seismic waves and echolocation use reflected waves to collect information about objects or places that cannot be directly observed.
• The electromagnetic spectrum, from longest wavelength to shortest wavelength, is radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays.
• Electromagnetic waves are transverse waves that can travel through a vacuum at the same speed, approximately `3.0 \times 10^8` metres per second.
• The regions of the electromagnetic spectrum differ in wavelength, frequency and energy; shorter wavelength radiation has higher frequency and higher photon energy.
• Ultraviolet, X-rays and gamma rays are ionising radiations because they can remove electrons from atoms and can damage living cells and DNA.
• At a boundary between materials, light can be reflected, transmitted, absorbed or a combination of these.
• Refraction happens when a wave changes speed as it enters a different medium, causing a change in direction if it enters at an angle to the normal.
• Filters transmit only a narrow range of wavelengths of light and absorb or reflect other wavelengths.
• All objects emit and absorb infrared radiation, and hotter objects emit radiation with shorter peak wavelengths and greater intensity.

• Identify transverse and longitudinal waves from diagrams by comparing particle vibration direction with energy transfer direction.
• Label wavelength, amplitude, compression and rarefaction accurately on wave diagrams.
• Calculate wave speed, frequency, wavelength or time period by selecting and rearranging `v = f\lambda` or `f = 1/T` with correct units.
• Describe sound as a longitudinal wave by explaining how particle vibrations create compressions and rarefactions through a medium.
• Construct ray diagrams for reflection using a normal line and the law of reflection, where the angle of incidence equals the angle of reflection.
• Construct ray diagrams for refraction at a boundary by showing light bending towards the normal when it slows down and away from the normal when it speeds up.
• Explain the apparent colour of objects by identifying which wavelengths are reflected, absorbed or transmitted.
• Predict the effect of colour filters by stating which wavelengths are transmitted and which are absorbed.
• Compare uses of electromagnetic waves by linking each region’s properties to applications such as communication, heating, imaging, sterilising or medical treatment.
• Analyse convex and concave lens ray diagrams by tracing principal rays to determine whether the image is real or virtual, magnified or diminished, and upright or inverted.