3 Waves

Use the following units: degree (°), hertz (Hz), metre (m), metre/second (m/s) and second (s)

Explain the difference between longitudinal and transverse waves

Know the definitions of amplitude, wavefront, frequency, wavelength and period of a wave

Know that waves transfer energy and information without transferring matter

Know and use wave speed = frequency × wavelength, v = fλ.

Use frequency = 1 ÷ time period, f = 1/T.

Use the above relationships in different contexts, including sound waves and electromagnetic waves

Explain why there is a change in the observed frequency and wavelength of a wave when its source is moving relative to an observer and that this is known as the Doppler effect

Explain that all waves can be reflected and refracted

Know that light is part of a continuous electromagnetic spectrum that includes radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray radiations, and that all these waves travel at the same speed in free space

Know the order of the electromagnetic spectrum in terms of decreasing wavelength and increasing frequency, including the colours of the visible spectrum

Explain some of the uses of electromagnetic radiations, including:

• radio waves: broadcasting and communications
• microwaves: cooking and satellite transmissions
• infrared: heaters and night vision equipment
• visible light: optical fibres and photography
• ultraviolet: fluorescent lamps
• x-rays: observing the internal structure of objects and materials, including for medical applications
• gamma rays: sterilising food and medical equipment

Explain the harmful effects of excessive electromagnetic-wave exposure: microwave internal heating, infrared skin burns, ultraviolet surface-cell damage and blindness, and gamma-ray cancer and mutation; describe simple protective measures.

Know that light waves are transverse waves and that they can be reflected and refracted

Use the law of reflection (the angle of incidence equals the angle of reflection)

Draw ray diagrams to illustrate reflection and refraction

Practical: investigate the refraction of light, using rectangular blocks, semi-circular blocks and triangular prisms

Know and use refractive index n = sin i ÷ sin r.

Practical: investigate the refractive index of glass, using a glass block

Describe the role of total internal reflection in transmitting information along optical fibres and in prisms

Explain the meaning of critical angle c

Know and use sin c = 1/n for critical angle c and refractive index n.

Know that sound waves are longitudinal waves that can be reflected and refracted

Know that the frequency range for human hearing is 20–20 000 Hz

Practical: investigate the speed of sound in air

Understand how an oscilloscope and microphone can be used to display a sound wave

Practical: investigate the frequency of a sound wave using an oscilloscope

Understand how the pitch of a sound relates to the frequency of vibration of the source

Understand how the loudness of a sound relates to the amplitude of vibration of the source