3. Waves

• Know: waves transfer energy without transferring matter

• Describe what is meant by wave motion as illustrated by vibrations in ropes and springs, and by experiments using water waves

• Describe the features of a wave in terms of wavefront, wavelength, frequency, crest (peak), trough, amplitude and wave speed

• Recall/use: for wave speed v = f λ

• Know: for a transverse wave, the direction of vibration is at right angles to the direction of propagation and understand that electromagnetic radiation, water waves and seismic S-waves (secondary) can be modelled as transverse

• Know: for a longitudinal wave, the direction of vibration is parallel to the direction of propagation and understand that sound waves and seismic P-waves (primary) can be modelled as longitudinal

• Describe how waves can undergo: (a) reflection at a plane surface (b) refraction due to a change of speed (c) diffraction through a narrow gap

• Describe the use of a ripple tank to show: (a) reflection at a plane surface (b) refraction due to a change in speed caused by a change in depth (c) diffraction due to a gap (d) diffraction due to an edge

• Describe how wavelength and gap size affects diffraction through a gap

• Describe how wavelength affects diffraction at an edge

• Define and use the terms normal, angle of incidence and angle of reflection

• Describe the formation of an optical image by a plane mirror and give its characteristics, i.e. same size, same distance from mirror, virtual

• State: for reflection, the angle of incidence is equal to the angle of reflection; recall and use this relationship

• Use simple constructions, measurements and calculations for reflection by plane mirrors

3.2.2.1Terms normal, angle of incidence and

• Define and use the terms normal, angle of incidence and angle of refraction

3.2.2.2An experiment to show refraction of

• Describe an experiment to show refraction of light by transparent blocks of different shapes

3.2.2.3Passage of light through a transparent

• Describe the passage of light through a transparent material (limited to the boundaries between two mediums only)

3.2.2.4Meaning of critical angle

• State the meaning of critical angle

3.2.2.5Internal reflection and total internal

• Describe internal reflection and total internal reflection using both experimental and everyday examples

3.2.2.6Refractive index, n, as the ratio of

• Define refractive index, n, as the ratio of the speeds of a wave in two different regions

3.2.2.7Refractive index: n = sin i / sin r

• Recall/use refractive index: n = sin i / sin r

3.2.2.8Critical angle relation: n = 1 / sin c

• Recall/use critical angle relation: n = 1 / sin c

3.2.2.9Use of optical fibres, particularly in

• Describe the use of optical fibres, particularly in telecommunications

• Describe the action of thin converging and thin diverging lenses on a parallel beam of light

• Define and use the terms focal length, principal axis and principal focus (focal point)

• Draw and use ray diagrams for the formation of a real image by a converging lens

• Describe the characteristics of an image using the terms enlarged/same size/diminished, upright/inverted and real/virtual

• Know: a virtual image is formed when diverging rays are extrapolated backwards and does not form a visible projection on a screen

• Draw and use ray diagrams for the formation of a virtual image by a converging lens

• Describe the use of a single lens as a magnifying glass

• Describe the use of converging and diverging lenses to correct long-sightedness and short-sightedness

• Describe the dispersion of light as illustrated by the refraction of white light by a glass prism

• Know the traditional seven colours of the visible spectrum in order of frequency and in order of wavelength

• Recall that visible light of a single frequency is described as monochromatic

• Know the main regions of the electromagnetic spectrum in order of frequency and in order of wavelength

• Know: all electromagnetic waves travel at the same high speed in a vacuum

• Describe typical EM spectrum uses: (a) radio waves: radio/TV, astronomy, RFID (b) microwaves: satellite TV, mobile phones, microwave ovens (c) infrared: grills, remotes, intruder alarms, thermal imaging, optical fibres (d) visible light: vision, photography, illumination (e) ultraviolet: security marking, fake banknote detection, sterilising water (f) X-rays: medical scans, security scanners (g) gamma rays: sterilising food/medical equipment, cancer detection/treatment

• Describe harm from excessive EM radiation: (a) microwaves: internal body-cell heating (b) infrared: skin burns (c) ultraviolet: surface-cell/eye damage, skin cancer and eye conditions (d) X-rays/gamma rays: mutation or cell damage

• Know: communication with artificial satellites is mainly by microwaves: (a) some satellite phones use low orbit artificial satellites (b) some satellite phones and direct broadcast satellite television use geostationary satellites

• Know: the speed of electromagnetic waves in a vacuum is 3.0 × 108 m/s and is approximately the same in air

• Know communication systems using EM radiation: (a) mobile phones/wireless internet use microwaves because they penetrate some walls and need short aerials (b) Bluetooth uses radio waves because they pass through walls but weaken (c) optical fibres use visible/infrared for cable TV and high-speed broadband because glass transmits them and they carry high data rates

• Know the difference between a digital and analogue signal

• Know: a sound can be transmitted as a digital or analogue signal

• Explain the benefits of digital signalling including increased rate of transmission of data and increased range due to accurate signal regeneration

• Describe the production of sound by vibrating sources

• Describe the longitudinal nature of sound waves

• State the approximate range of frequencies audible to humans as 20 Hz to 20 000 Hz

• Know: a medium is needed to transmit sound waves

• Know: the speed of sound in air is approximately 330–350 m/s

• Describe a method involving a measurement of distance and time for determining the speed of sound in air

• Describe how changes in amplitude and frequency affect the loudness and pitch of sound waves

• Describe an echo as the reflection of sound waves

• Define ultrasound as sound with a frequency higher than 20 kHz

• Describe compression and rarefaction

• Know that, in general, sound travels faster in solids than in liquids and faster in liquids than in gases

• Describe the uses of ultrasound in non- destructive testing of materials, medical scanning of soft tissue and sonar including calculation of depth or distance from time and wave speed