Electromagnetic Spectrum

Noadswood Science, 2011

Electromagnetic Spectrum

• To know the electromagnetic spectrum, and to research how each wavelength can be used

Tuesday, April 18, 2023

Electromagnetic Spectrum

• What is the electromagnetic spectrum?

• What is the difference between this and an electromagnetic wave?

Electromagnetic Spectrum

• The properties of electromagnetic waves (EM waves) change as the frequency (wavelength) changes

• They can be split into seven basic types – all of these EM waves form a continuous spectrum (the different regions merge into each other)

• We can only detect a narrow range of EM waves (visible light)

Electromagnetic Radiation

• Electromagnetic radiation travels as waves and transfers energy from one place to another

• All electromagnetic waves can travel through a vacuum, and they all travel at the same speed in a vacuum

• The types of radiation that occur in different parts of the spectrum have different uses and dangers, which depend on their wavelength and frequency

Electromagnetic Spectrum

• The electromagnetic spectrum is made up of the following: -• Radio waves (1m – 104m) – lowest frequency, longest

wavelength• Microwaves (10-2m (3cm))• Infra-red (10-5m (0.01mm))• Visible light (10-7m)• Ultra violet (10-8m)• X-rays (10-10m)• Gamma rays (10-12m)– highest frequency, shortest wavelength

Electromagnetic Spectrum

• The electromagnetic spectrum is made up radio waves; microwaves; infra red; visible light; ultra violet; X-rays; and gamma rays

Visible Light

• White light can be split up using a prism to form a spectrum• The light waves are refracted as they enter and leave the

prism – the shorter the wavelength of the light, the more it is refracted

• As a result, red light is refracted the least and violet light is refracted the most, causing the coloured light to spread out to form a spectrum

Dispersion

• The different colours of light have different wavelengths, this means they are bent (refracted) by different amounts

Red light is refracted least because it has the longest wavelength

Violet light is refracted the most because it has the shortest wavelength

Spectrum

• Visible light is just one type of electromagnetic radiation

• There are various types of electromagnetic radiation, some with longer wavelengths than visible light and some with shorter wavelengths than visible light

• As the wavelength of EM radiation changes, so its interaction with matter changes (particularly how the wave is absorbed, reflected or transmitted)

Electromagnetic Spectrum

• Your task is to research each of the electromagnetic waves – what are they generally used for and are there any dangers associated with them?

• The research is for your own notes, but try and be concise and fit them all onto one page (two at most) – try and avoid simply using text, instead being as creative as possible: -• Radio waves

• Microwaves

• Infra red

• Visible Light

• Ultra violet

• X-rays

• Gamma rays

Electromagnetic Spectrum

Frequency Type of EM Typical use Wavelength

Highest Gamma rays Killing cancer Shortest

X-rays Medical imaging

Ultra violetDetecting forged

banknotes

Visible light Seeing

Infra redOptical

communications

Microwaves Cooking

Lowest Radio wavesRadio and TV

signalsLongest

Gamma Rays

• Gamma waves have a very high frequency• It mostly passes through skin and soft tissue, but

some of it is absorbed by cell• Gamma radiation is used, among other things, for

the following purposes: -• To sterilise surgical instruments• To kill harmful bacteria in food• To kill cancer cells (lower doses of gamma

radiation could lead to cells becoming cancerous)

X-Rays

• X-rays have a lower frequency than gamma radiation• X-rays mostly pass through skin and soft tissue, but

they do not easily pass through bone or metal so X-rays are used to produce photographs of bones to check for damage such as fractures

• They are also used in industry to check metal components and welds for cracks or other damage

• Lower doses of X-rays can cause cells to become cancerous, so precautions are taken in hospitals to limit the dose received by patients and staff when X-ray photographs are taken

Ultra Violet

• Ultraviolet radiation is found naturally in sunlight – our skin responds to it by turning darker in an attempt to reduce the amount of ultraviolet radiation that reaches deeper skin tissues

• Darker skins absorb more ultraviolet light, so less ultraviolet radiation reaches the deeper tissues (this is important because ultraviolet radiation can cause normal cells to become cancerous)

• Ultraviolet radiation is used in: -• Sun beds• Security pens• Fluorescent lights (coatings inside the tube or

bulb absorb the ultraviolet light and re-emit it as visible light)

Infra red

• Infrared radiation is absorbed by the skin and we feel it as heat – it is used in heaters, toasters and grills

• It is also used for television remote controls and in optical fibre communications

Microwaves

• Microwaves are mainly used for cooking and communications

• Microwaves with certain wavelengths are absorbed by water molecules and can be used for cooking – water in the food absorbs the microwave radiation, which causes the water to heat up and cook the food

• The water in living cells can also absorb microwave radiation (as a result, they can be killed or damaged by the heat released)

Microwaves

• Microwave radiation can also be used to transmit signals such as mobile phone calls – microwave transmitters and receivers on buildings and masts communicate with the mobile telephones in their range

• Certain microwave radiation wavelengths pass through the Earth's atmosphere and can be used to transmit information to and from satellites in orbit)

Radio waves

• Radio waves are used to transmit television and radio programmes (television uses higher frequencies than radio)

• A radio programme receiver does not need to be directly in view of the transmitter to receive programme signals – for low frequency radio waves diffraction can allow them to be received behind hills, although repeater stations are often used to improve the quality of the signals

• The lowest frequency radio waves are also reflected from an electrically charged layer of the upper atmosphere, called the Ionosphere meaning they can reach receivers that are not in the line of sight

Radio waves

• Radio waves are used to transmit television and radio programmes (television uses higher frequencies than radio)