(c) The electromagnetic spectrum

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.