Download Light - Wando High School

Light
WHAT IS LIGHT?
Light is…
A form of energy that travels as a wave.
An example of a transverse wave
One type of electromagnetic wave.
The only visible part of the electromagnetic spectrum.
How are colors of visible light different?
What makes red light look red? Or blue look blue?
Red has the longest wavelength of visible light (the top most waves in the pic)
Violet has the shortest wavelength of visible light
Frequency and Energy
The color with the lowest frequency wave that is visible is
.
The color with the highest number of waves per second is
.
Energy:
The higher the frequency, the higher the energy
Red= lowest energy
violet= highest energy
What makes a light bright
The amplitude of the wave determines the brightness of the light
Higher amplitude= brighter light
Which of the following would be brighter?
Would they be the same color?
YES, Same wavelength!
Waves that we CANNOT see
Visible light is a tiny part of the many types of waves in the electromagnetic spectrum
We cannot see wavelengths longer than red…
or shorter than violet
A little practice
1. What type of electromagnetic waves has the most energy?
2. What type has the longest wavelength?
3. What type has the highest frequency?
4. What visible light has the longest wavelength?
5. What visible light has the lowest frequency?
1) gamma 2(radio waves 3) gamma 4) red 5) red
White light
White light can be made of all colors.
If all colors (ROY G BIVTM) of light are mixed, we see white light.
What is black?
Black is the absence of light.
Why is space black?
The sky is FULL of stars…
So why is space black? (Even if you went above the Earth’s atmosphere during the day)
There is nothing in space to reflect light!
Except, of course, planets, moons, and rocks in space.
Speed of Light
Light travels 186,000 miles per second.
Light is so fast that in 1 second it could speed around the Earth about 7 ½ times!
ALL light and all electromagnetic waves travel the exact same speed!
Is red or green light faster? Same!
Infrared or gamma rays faster? Same!
More practice with EM waves
Which visible light…
1) Is the second longest in wavelengths?
2) 2nd in most energy of visible colors? (of the 7 basic colors)
Put these in order from
3) longest to shortest wavelength…
Green, x-rays, orange, microwaves
4) Highest energy to lowest energy…
Green, violet, UVB, x-rays, infrared
5) Lowest to highest energy…
Yellow, microwaves, x-rays, infrared, UV, blue,
1)orange 2) indigo 3) microwaves, orange, Green, x-rays 4) x-rays, uvB, violet, green, infrared
5) microwaves, infrared, yellow, blue, UV
Putting Light to work (p. 42-43)
The light given off by something (like a star) can tell you what elements are in it.
Different elements will show up as bright spectral lines in a star’s spectrum.
Missing spectral lines can tell you about what the light has passed through on the way to Earth.
Missing spectral lines can also tell you what elements are within the star. These elements are what is absorbing the
light .
Studying spectral lines led to the discovery of over 70 elements in the sun- including helium which was first found
in the sun. Helios means “Sun”.
Colors of the Stars (p. 114-115)
Stars can be different colors.
Bluish stars are hottest, reddish are cooler
Spectral class-In order from hottest to coolest…
Oh, Be a fine girl, kiss me!
O- bluish
B- bluish white
A- white
F- whitish yellow
G- yellow
K- orange
M- Red
Within a Class, there are subclasses of 0-9
0 being the hottest
Our sun- G2
To the End of the Dial (p. 44-45)
The non-visible parts of the spectrum are important to astronomers.
Infrared radiations is detected as heat.
IR is used to view gas and dust.
Ex. around newborn stars in galaxies..
The microwave parts of the spectrum can show the background radiation of the universe- revealing its shape and
other facts.
Active galaxies produce synchrotron radiation, a powerful radio wave.
Longer wavelengths have trouble getting through the atmosphere, thus instruments to read these must be high
altitude or in space.
Radio waves are so long that a very large dish or a system of dishes far apart are used to study them.
Radio waves reveal much about the universe.
They can help detect neutron stars.
High Energy Astronomy (p. 46-47)
Ultraviolet, X-rays, and gamma rays…
are all high energy invisible waves with short wavelengths.
Some events and objects in space are best detected at these wavelengths.
Ultraviolet C waves and all waves shorter are blocked by our atmosphere (ozone).
Equipment must be in space to pick these up.
UV (a and b)- cause of sunburn, produced by very hot gases in space.
X-rays- made by “active” galaxies that have bright centers. “Feeding” black holes may create them.
Gamma rays- most energetic/shortest waves of all. Produced by very violent sources (supernova, quasars, pulsars)
Gamma Ray bursts- are studied often
Light Diffusion
Summary
Light spreads out in a sphere as it travels.
This same amount of light must take up more space as it spreads
This makes it weaker as it spreads (like peanut butter on toast).
This means the amplitude lowers as light travels through space.
Real life example question:
Why don’t stars light up the sky like the sun does? Diffusion! (over great distances)
Diffusion of light
As light travels through space, it spreads out, making it less bright as it takes up more area.
Blue Skies and Colorful sunsets