Published on February 15, 2014
Electromagnetic Radiation Sarah Jones scienceisbeauty.tumblr.com
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
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. • The next two slides – crystals on a speaker.
Wave Properties www.schoolphysics.co.uk www.genesis.net.au
• 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
Electromagnetic Radiation • James 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.
• 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
Radio Waves • Are 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. • Short-wave radio signals can be transmitted long distances. The waves are beamed upwards and are reflected back to earth by the ionosphere. www.arairwaves.com
• FM signal is about 3m wavelengths. • AM signal is about 100m wavelengths. • AM radio waves can travel around large obstacles and travel further than FM, however, they are lower quality and often suffer from interference. www.pfnicholls.com
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
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
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 lightsensitive 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. • People working with x-rays use lead shields and monitor exposure levels. www.sentara.com
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. • 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
The Visible Spectrum
Colour • Visible light (white light) consists of different colours – each has a different wavelength and frequency. ROY – G – BIV • The splitting of white light is called dispersion. cnx.org
• Objects tend to absorb some wavelengths and reflect others.
The perceived colours under white light, yellowish light, bluish light, and very red light. practicalpainter.blogspot.com
Primary Colours – Red, Green and Blue Secondary Colours – Magenta, Cyan and Yellow
Colour Printing www.novaprinting.ca
Polarisation of Light physicsnet.co.uk www.physics.louisville.edu
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