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Science 8 – Physical Science
OpticsChapters 4-6
4.2 Properties of Visible Light
Science 8 – Physical Science - Optics
Demo - Prism
• What do you observe?• Why?
gallery.hd.org
Science 8 – Physical Science
OpticsChapters 4-6
The Wave Model of Light
• Scientists often use models to help represent something or to understand it better so we can make predictions.
• The wave model of light says that “light is a type of wave that travels through empty space and transfers energy from one place to another.”(pg. 145)
kidsgeo.com
Refraction of a Wave
• As water approaches the shore, the direction of the wave changes.
• This is called refraction:“Refraction is the bending or changing direction of a wave as it passes from one material to another.” (pg. 145)
• Student Demo
meted.ucar.edu
Refraction of Light
• The wave model of light says that light behaves like a wave.
• Therefore light also refracts when it enters a new medium.
• So what happened with the prism?
chemicalparadigms.wikispaces.com
The Colours of the Rainbow
• White light (from the sun, or the overhead projector) is made up of many different wavelengths.
• These wavelengths go at different speeds when they enter a new medium.
• Some of them will “slow down” more than others and so they get separated and we observe colours.
www.fotolia.com/id/10579816?by=similia
Rainbow Formation
• Look at Figure 4.11 on pg. 146.
• Rainbows are formed in the same way.
• The white light enters the water droplet and the different wavelengths separate out showing us the different colours.
webecoist.com
Colour and Reflection
math.ubc.ca
Reflection and Absorption
• “Reflection occurs when a light wave strikes an object and bounces off.” (pg. 148)
• The colours that we see result from some wavelengths of light being absorbed and others being reflected.
• Red, Blue, and Green are the primary additive colours. All other colours can be made by combining those.
colourtherapyhealing.com
4.3 Light and the Electromagnetic Spectrum
Science 8 – Physical Science - Optics
Demo – Seeing the Invisible
Radiant Energy
• The Sun emits, or radiates, energy in the form of different waves.
• This energy is called radiant energy.
• In these waves, electrical and magnetic fields vibrate. Therefore it is called electromagnetic radiation. space.about.com
The Electromagnetic Spectrum• The light we see is
referred to as the visible spectrum.
• This is only a small part of the electromagnetic spectrum.
• There are other waves that have larger and smaller wavelengths than the visible spectrum.
lcse.umn.edu
Figure 4.20
Radio Waves
• Radio waves have the longest wavelength and the lowest energy and frequency compared to all other EM waves.
• Radio waves are commonly used for radio and television broadcasting (Fig. 4.21) as well as MRI imaging.
ecrc-pt.com
businessweek.com
Microwaves• Microwaves have shorter
wavelengths and higher frequencies than other radio waves.
• Microwaves are strongly absorbed by water particles so are used in microwave ovens to heat foods that contain water.
• They are also used in telecommunications and radar.
renthire.com
mydreamcourse.co.za
atmos.washington.edu
Infrared Waves• Infrared waves have
wavelengths just longer than the visible colour red.
• Infrared waves are used in remote controls and to read CD-ROMs.
• Infrared radiation is also known as heat radiation because everything with some heat energy emits infrared waves.
useit.com
commons.wikimedia.org
imaging1.com
Ultraviolet Waves
• This type of electromagnetic radiation has a shorter wavelength and therefore higher frequency and energy than visible light.
• It enables your body to produce vitamin D, which is needed for healthy bones and teeth.
• UV waves are used in forensic science to study finger prints.
• They also kill bacteria in food, water, and medical supplies.
• Overexposure can lead to sunburn, skin cancer, and damage to the eye.
X Rays
• X rays are commonly used to photograph teeth and bones.
• Other uses include airport security and inspection of the inside of machines.
hahahaimontheinternet.com
dvice.com
Gamma Rays
• Gamma rays are the shortest wavelength and highest frequency and energy wave.
• Gamma rays are formed in nuclear reactions.
• They are used in radiation therapy to kill cancer cells.
stfc.ac.uk