Learning Goals:
Many technologies produce light by converting other forms of energy.
Light is energy and travels like a wave.
Success Criteria:
I can...
...list and describe the methods by which light is made.
...indicate that light is an energy that travels like a wave.
...draw and explain the characteristics of a wave.
...define, describe and provide examples related to the electromagnetic spectrum.
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The Uses of Light
Brainstorm the uses that we have for light.
Producing Light
Incandescence
Incandescence is the light produced by a hot object. It is made by:
- burning fuel - inefficient as most of the chemical energy stored in the fuel is converted into heat
- running electricity through a metal filament (like in a traditional light bulb) until it gets so hot it glows – also inefficient due to 90% loss of energy as heat.
Luminescence
Luminescence the production of light without heating. It is made by:
- chemiluminescence – light released during chemical reactions (glow sticks).
- electric discharge – gas encased in a glass tube emit light when it interacts with a stream of electrons (yellow coloured sodium vapour street lights).
- fluorescence – similar to electric discharge, except the emitted light is UV (fluorescent lights).
Wave Theory of Light
Light reflects off an object toward our eyes and forms an image on our retinas.
Light has many wave-like properties:
It can be:
- reflected (bouncing off a surface)
- refracted (change in speed of the wave as it passes from one medium to another)
- diffracted (bending of waves around a barrier)
However, light requires no medium (it can travel through a vacuum).
Since the similarity of light to a wave is greater than the difference, we accept the wave theory of light – light travels in the form of electromagnetic waves, which are similar to water waves.
Electromagnetic Spectrum
The electromagnetic spectrum consists of waves, from long wavelength to short wavelength.
From longest to shortest wavelength:
- Radio waves are used for TV signals, cell phones and satellite communication. Also used in MRI machines to make soft tissues appear visible
- Microwaves are used to heat food, to measure speeds via radar and for communication.
- Infrared (IR) waves are experienced as heat. IR can be used in thermal imaging.
- VISIBLE LIGHT is a very small region in the EM spectrum (it is the rainbow - ROYGBIV)
- Ultraviolet (UV) rays travel from the Sun. Also used to disinfect drinking water and in DNA analysis.
- X-rays are used to get images of bones. Also used to scan luggage at the airport
- Gamma rays can penetrate human tissue, so they are used to kill cancer cells.
Let's make like a light and shine.
