Electromagnetic Radiation
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Transcript of Electromagnetic Radiation
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scienceisbeauty.tumblr.com
Electromagnetic RadiationSarah Jones
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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
thejetlife.com
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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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http://fabianoefner.com
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w3.shorecrest.org
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Wave Properties
www.schoolphysics.co.uk
www.genesis.net.au
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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.
www.schoolphysics.co.uk
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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.
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The changing magnetic field and electric fields travel through space as transverse waves at right angles – this is known as an electromagnetic wave.
mysite.du.edu
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www2.astro.psu.edu
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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.
www.globalspec.com
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www.noaa.gov
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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
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FM signal is about 3m wavelengths.AM signal is about 100m wavelengths.
www.pfnicholls.com
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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.
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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.
www.harveynorman.com.au
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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.
en.wikipedia.org
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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
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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.
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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.
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Fluorescent minerals under ultraviolet light
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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).
www.sentara.com
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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.
apod.nasa.gov
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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.
www.geripal.org
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The Visible Spectrum
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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.
cnx.org
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Objects tend to absorb some wavelengths and reflect others.
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practicalpainter.blogspot.com
The perceived colours under white light, yellowish light, bluish light, and very red light.
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Primary Colours – Red, Green and BlueSecondary Colours – Magenta, Cyan and Yellow
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Colour blindness
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Colour Filters
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Colour Printing
www.novaprinting.ca
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Polarisation of Light
www.physics.louisville.edu
physicsnet.co.uk
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Light Interference