Electromagnetic Radiation

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Electromagnetic RadiationSarah Jones

Light• Light is a form of energy known as

electromagnetic radiation.• Light travels as an electromagnetic wave.• Light travels through the vacuum of space –

unlike sound.• It travels at 300 000 km/s

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Wave Motion

• Wave motion is the transfer of energy without matter.

• Transverse wave e.g. how an ocean wave travels to the shore while a boat just moves up and down.

• Longitudinal wave – Sound wave i.e. the particles that make up the wave move in the same direction the wave is travelling.

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Wave Properties

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• Frequency – number of waves produced each second (measured in Hz).

• Wavelength (λ) – the distance between two successive waves (measured in m).

• Amplitude – is the maximum distance a wave extends beyond its middle position.

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Electromagnetic RadiationJames Maxwell (1831-1879) proposed that a changing electric field could create a changing magnetic field – and this would create a changing electric field – these fields would continue to generate each other.

The changing magnetic field and electric fields travel through space as transverse waves at right angles – this is known as an electromagnetic wave.

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• Electromagnetic radiation includes visible light, microwaves and x-rays.

• Solar flares on the Sun release large amounts of energy across the electromagnetic spectrum.

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Radio Waves• Produced by vibrating or oscillating electrons

in a transmitting aerial.• They can travel large distances.• Long and short-wave radio signals are used in

communication. www.arairwaves.com

FM signal is about 3m wavelengths.AM signal is about 100m wavelengths.

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• Short-wave radio signals can be transmitted long distances. The waves are beamed upwards and are reflected back to earth by the ionosphere.

• AM radio waves can travel around large obstacles and travel further than FM, however, they are lower quality and often suffer from interference.

Microwaves• Microwaves are absorbed by water, fats and

sugars in foods. • Microwaves make food molecules vibrate and

heat the food up.• Glass, paper and plastics don’t absorb

microwaves and metal reflects microwaves.

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Infrared Radiation• Heat from the sun is IR.• IR is close to red light in the visible spectrum

(infra – below, therefore frequency below red light).

• Objects with a temperature above 0 Kelvin (-273.15°C) emit IR.

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Visible Light• Light from the Sun is essential for life on Earth.• Visible light (white light) consists of different

colours – each has a different wavelength and frequency.

ROY – G – BIV • Most humans can see all of these wavelengths

(colours) but have the greatest sensitivity to the green range of the spectrum

The Visible Spectrum• Visible light is a small part of the spectrum

that can be seen by the human eye.• The wavelengths can be detected by the light-

sensitive cells called rods and cones present in the eye.

Ultraviolet Light• UV light is radiation with a higher frequency than

violet light (ultra – beyond).• Sunlight contains UV light.• You cannot see UV light – it does cause sun burn.• Many object fluoresce under UV light.

Therefore, they absorb UV light and emit visible light.

• UV light is used to sterilise objects.

Fluorescent minerals under ultraviolet light

X-Rays• Wilhelm Roentgen discovered x-rays in 1895.• X-rays can penetrate objects, therefore, they

are useful in finding flaws and checking structure.

• The high energy of the radiation can damage cells and tissues

(wear lead shileds).

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Gamma Rays• Wavelength of about one hundred billionth of

a metre.• They can only be stopped by thick sheets of

lead or concrete.• They are produced in the making of nuclear

power.

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Medically a patient can be injected with a small amount of radioactive material that emits gamma rays – this can then be detected by a positron emission tomography (PET) scanner.

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The Visible Spectrum

ColourVisible light (white light) consists of different colours – each has a different wavelength and frequency.

ROY – G – BIVThe splitting of white light is called dispersion.

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Objects tend to absorb some wavelengths and reflect others.

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The perceived colours under white light, yellowish light, bluish light, and very red light.

Primary Colours – Red, Green and BlueSecondary Colours – Magenta, Cyan and Yellow

Colour blindness

Colour Filters

Colour Printing

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Polarisation of Light

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Light Interference