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?

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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)

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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

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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?

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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.

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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.

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Colour and Reflection

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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.

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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.

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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.

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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.

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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.

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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.

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