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Light and Color Midterm 1
Light and Color Midterm 1
43
Physics
Undergraduate 2
04/25/2012

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Cards

Term
What is the speed of light?
Definition

o   Nothing travels faster than light, 186,000 miles/second

 

Term
What is a wave?
Definition

 

o   A wave is a propagating disturbance through a medium

 

Term
What happens when 2 waves meet?
Definition

Constructive interference:2 waves meet, make a bigger wave, and continue on their way

Term
What is destructive interference?
Definition
Opposite crest and trough cancel out
Term
What does in phase mean? Light/dark?
Definition
It is constructive, they match up and make a bigger wave and is light
Term
What does out of phase mean?
Definition
They are opposite and cancel eachother out and is dark
Term
In terms of amplitude, what is bright, dim, and no light?
Definition

Large amplitude =bright

Low amplitude=dim

zero amplitude=no light

Term
What is wavelength
Definition
distance between two successive peaks
Term
What is frequency?
Definition
Number of peaks passing per second.
Term
Large frequency=?
Definition
Small wavelenths
Term
How do you find the speed of a wave?
Definition
Speed = wavelength x frequency
Term
What is the fastest traveling EM wave?
Definition
They all travel at the same speed but have different wavelengths
Term
What is the progression of wave lengths for EM waves?
Definition

o   Cosmic rays-gamma rays-xrays-ultra violet rays-visible light-infared-satellite communications-weather satellites-cellular phones-television-FM radio-AM radio-radio navigation-power transmission

 

Term
What is resonant frequency? What happens?
Definition
The frequency in which they like to be shaken. If the wave shakes the object at its resonant frequency than it absorbs that energy
Term
What happens when it is on resonance? Off resonance?
Definition

On resonance- wave absorbed

Off resonance- wave transmitted

Term
What can you use gamma rays for?
Definition

o   borderline protection(looking for nuclear things), see blood flow, nuclear explosions, sendoff rockets(could)

 

Term
What can you use xrays for?
Definition

o   Xrays: on resonance with skin off resonance with bone so you can see bone not skin, CAT Scan, see teeth(on resonance), see tumors, see black holes, tell where ozone is

 

Term
What can you do with UV rays?
Definition

o   Ultra-violet: skin is on-resonance (waves aborbed by skin/skin burn/skin tan) eye lens is on resonance(waves absorbed by lens/don’t reach the retina(can’t see UV). Water is on resonance. We give off UV b/c we’re hot and environment is cold,

 

Term
What is hard UV?
Definition
Smaller wavelengths, causes skin burn, doesn't pass through glass
Term
What is soft UV?
Definition
Longer wavelengths, doesn't cause skin burn, passes through glass
Term
What does visible light do?
Definition

o   Visible light: the narrow range of wavelenths which are on resonance for the human retina. Different wavelengths are on resonance for different photo recpetors allowing us to see color. 400nm-700nm

 

Term
What does Infra-red do?
Definition

o   Infra-red: human skin is on resonance(waves absorbed by skin, energy rises, skin feels warm) human retina is off resonance(waves pass thru with no interaction, we don’t see it) liquid is on resonance. Makes us feel warm. Insects can see it because they don’t have liquid eyes. Remotes use it, they use it for eye exams, detect radiation, see warm and cold currents, see if you are lying

 

Term
What do microwaves do?
Definition

o   Microwaves: shakes the water to heat it up, defrost means less amplitude, water is on resonance, absorbs energy, heats up. (more efficient than conventional ovens which heat air)

 

Term
How can you use radiowaves?
Definition

o   Radiowaves: radar (the time it takes it to come back tells the chip the speed of the car), soundwaves are sent out to detect objects under water-sonar, Whales use sonar to see, AM (amplitude modulated) FM (frequency modulated), can see through clouds up to 1m, radar used to detect storm front b/c they bounce off clouds with 100km wavelength so you can map where the clouds are

 

Term
What happens when you raise the temperature?
Definition

o   Raise temperature-charges wiggle faster-wave frequency increases. As you raise temp, glows red than orange, can determine temp from color. Increase temp-range of frequency increase-eventually white light.

 

Term
What type of light passes through clouds?
Definition
UV passes through clouds, visible light doesn't
Term
What happens when radiation passes through the atmosphere?
Definition
Much of the IF is absorbed in the water of the atmosphere
Term
What happens to the UV in the atmosphere?
Definition
It is absorbed
Term
How thick is the ozone?
Definition
1/8th of an inch
Term
What is the greenhouse effect?
Definition
Light passes in and is absorbed by the plant, the plant gives off infrared, the infrared wont pass through the glass and that creates the heat. UV can't pass thru glass either
Term
How is the greenhouse effect applied to global warming?
Definition
The carbon dioxide acts like glass
Term
How does light make color?
Definition
It has to go through the atmosphere
Term
What is incandescence?
Definition
Heat up an object and gives off light ex.the sun, coal
Term
What is an ARC-lamp?
Definition
Electrons accelerated by voltage, smash into carbon plate, heating it up. Very bright, used in theaters
Term
What is a light bulb?
Definition
Incandescent. Electrical resistance causes filament to warm up, filament then radiates. Very inefficient because it peaks in the infra-red
Term
What is a tungsten-halogen light?
Definition
Higher temperature with a containing halogen which makes the filament take longer to evaporate
Term
Which light is "good light" and why?
Definition
florescent because it radiates more light, less heat, voltage causes electrons to accelerate hitting gas molecules, causing them to wiggle. The molecule wiggles at its resonant frequency gives off light at the resonant frequency
Term
What type of color do these gasses give off? Neon? Mercury? Krypton?
Definition
Neon= red-orange. Mercury=blue-green, Krypton= pale blue
Term
What are high intensity discharge lamps?
Definition
Mercury lamps. Last 1000 years. Pale blue tint that lasts really long, only light no heat, efficient but mercury is really toxic
Term
What is a florescent tube?
Definition
Not incandescent, the shaking creates light. Electrode voltage accelerates electrons. These collide with gas molecules which shake on resonance, giving off UV radiation, phosphorous coating converts UV to visible
Term
Why don't people like florescent light?
Definition
It is more harsh, it gives out radiation at specific times unlike tungsten which is steady like the sun
Term
When do you use florescence?
Definition
For tagging molecules, art authenticity, police finger printing, and find it in nature
Term
Where do you find natural light that is not incandescent?
Definition
Lightening is not incandescent it is more like the efficient tubes, doesn't require heat for light. The northern lights aren't incandescent either
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