1. Light & Colors Chapters 27 & 28
Test Review for
Light & Colors Chapters 27 & 28

2. What is light? Light is created by vibrating charged particles
It is a transverse wave
It is the only wave that does not need a medium to travel through.

3. Speed of Light Time the appearance of the following image: Symbol is c
3 x 108 m/s or
300,000,000 m/s
A constant (when in a vacuum or atmosphere)
Average speed of light slows down in different materials due to time delays between absorption and re-emission within the material (you won’t need to know how to calculate this).

4. Equations Stop your whining! Same equations as the last unit v=d/t
v=λf
This time though, replace the v with c!
c=d/t
c=λf

5. Practice
It takes sunlight 8 minutes to travel to Earth. How far away is the sun?
First convert 8 minutes to seconds
8 minutes x 60 seconds/minute = 480 seconds
Now plug this into d=ct
d=3x108 m/s x 4.8x102 s
d=1.44 x 1011 m (144 million kilometers)

6. Practice
What is the frequency of violet light with a wavelength of 400 nm (4 x 10-7 m)?
Rewrite c=λf to f = c/λ
f = (3x108 m/s) / (4x10-7m)
7.5 x 1014 Hz

7. Shadows Created by OPAQUE objects blocking light.
Umbra: dark center, all light is blocked
Penumbra: fuzzy edges, some light is blocked

8. Sun, Earth, Moon, & Shadow

9. Electromagnetic Waves
Technical (read fancy) name for all light, including visible light.
All EM-waves travel at the same speed
They are defined by their different frequencies and wavelengths.

10. Electromagnetic waves
Increasing frequency 
Decreasing wavelength 
Increasing energy 

11. Electromagnetic Waves
Objects can be opaque to some EM waves but translucent to others.
Windows:
Can you see through them?
Can you get sunburned
through one?
Can infrared pass through them? (Look at the glasses above)

12. Inverse Square Law If you double your distance from the light:
The illuminance of the light is quartered.
If you triple your distance from the light:
The illuminance of the light will be 1/9th of the original brightness
If you halve your distance from the light:
The illuminance of the light is quadrupled.
Illuminance ~ 1/distance2

13. Polarization Natural light is randomly polarized.
Polarizers block light waves oscillating in one direction.
Reduces brightness of light by 50% for the first polarizer.
Second polarizer at 90o of first polarizer will block all light.
Reflected light/glare
are horizontally
polarized

14. Colors - Additive Primary colors - red, blue, green
White objects reflect all light.
Black objects absorb all light.
Blue objects reflect BLUE light
and absorb all other light.
All other light colors are made of the three primary colors.
Complementary colors: the two colors that can be added together to make white light.

15. Additive colors
Use of additive colors:

16. Subtractive (pigment) colors
Depends on colored light being subtracted.
Primary colors: magenta,
cyan, and yellow.
Absorb one primary color of
light and reflects two.
Filters subtract all light except
for the color of the filter.
Pigments/dyes absorb all
colors except for the few they reflect.

17. Subtractive Colors A red shirt under magenta light: red
A green book under blue light: black
Used by: