Unit 7: Light
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Light is an Electromagnetic Wave
• Electromagnetic wave (EM waves) can travel through
a vacuum (like space) or through a medium (like water or wood).
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EM waves carry energy!
We can classify EM waves based on their wavelength and frequency.
• What does an electromagnetic wave look like?
It consists of alternating magnetic and electric fields at right angles to each other. But what does that mean?
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Tah DAH!
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We call this radiation­­the emission of energy in the form of EM waves
Where do electromagnetic waves come from?
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Origin of an electromagnetic wave
Energy
>photon
>
+ +
electron
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So, the electrons gain energy and move farther away from the nucleus. As the electron falls back to its original position it releases energy. From this release a photon is produced.
A photon is a special particle of electromagnetic waves. Photons are not something you can "feel" but because EM waves act as a wave or particles we say that they are made up of a stream of particles called photons
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Light can travel in 2 ways:
• as a particle or
REALLY?!
• as a wave
This means that light has both wave­like and particle­like properties and travels in a STRAIGHT line
• When does it act like a particle?
Light acts like a particle when you look in a mirror because it bounces off it.
• When does it act like a wave?
Light acts like a wave when it goes through materials like glass, water, etc. 9
Light can be transmitted, absorbed, or scattered.
Absorption: The transfer of energy carried by light waves to particles of matter
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Scattering: the release of light energy by particles of matter that have absorbed energy 11
Transmission: Light passing through a medium
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Light can be Reflected­­ a wave bounces off an object.
This is what happens when you see yourself in a mirror!
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light E.M. Wave reflection magnetic fields
electric fields
transmission absorption 14
Refraction­­ the bending of a wave as it travels from one medium to another when it hits it at an angle
This occurs because of a change in wave speed
• Will not occur if the wave
hits the surface perpendicular
to the new medium. Which means
that it only works if the wave is travelling at an angle!
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Diffraction­­
is the bending of waves around a barrier or through an opening
The amount depends on the ____wavelength________ of the wave and the __size__ of the barrier
The edges of shadows are fuzzy because of the diffraction of light on the edge of your body.
Let's draw This!
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Let's review Interference!
• 2 types:
Constructive:
2 crests/troughs
overlap
Destructive:
a crest and trough
overlap
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Electromagnetic Spectrum
R
M
I
V
U
X
G
Radio
Microwaves
Infrared
Visible light
Ultraviolet
X­rays
Gamma Rays
longest wavelength
shortest wavelength
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Come up with your own Mnemonic device to remember the order of the spectrum
Raging
Martians
Invade
Violently
Using
×­ray
Guns
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Radio Waves
Have the longest wavelengths and lowest frequencies
Has the lowest energy
Used to transmit radio and television signals. Also used in telescopes to determine the locations of stars and galaxies.
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Microwaves can be used to cook food because they give kinetic energy to water molecules which, in turn, heats up the matter next to it.
Shorter wavelength &
higher frequency than
Radio waves.
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Infrared Waves
Just below the visible light spectrum, so their wavelengths are longer and their frequencies are lower.
Lower energy than visible light
We feel them as heat.
Military, police, and firefighters use infrared goggles to locate people in buildings and see at night
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Visible Light
ROY G BIV
Red has the lowest frequency and longest wavelength and therefore a lower energy
Violet has the highest frequency and shortest wavelength of the colors in the visible light spectrum and therefore a higher energy
Anything you can see! Cameras, mirrors, flashlights, etc
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Ultra Violet Light
Has a higher frequency and shorter wavelength than visible light and also higher energy.
UV bulbs are used in tanning booths and are produced by the sun. UV rays can cause skin cancer. Since it is produced by the sun, you always need to wear sunblock because the UV light can make it through the clouds even on an overcast day
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X­Rays
Short wavelengths, high frequency, and high energy
Used to make images of bones within the body. Can be dangerous if overexposed
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Gamma Rays
Shortest wavelength, Highest Frequency
Highest Energy
These wavelengths are smaller than atoms
Used to treat cancer in patients, however overexposure is extremely dangerous
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Attachments
allenarray from theperfectsilence.com