1. 6th Grade – Sound and Light (Mod. J) – Unit 3 Lessons 1 & 2

2. The Nature of Light Light travels in waves Do not need a medium
Disturbances in electric and magnetic fields
Transfer of energy as electromagnetic waves is called radiation
EM waves all move at the “speed of light” through empty space
300,000,000 m/s

3. Color Different colors of light because of different wavelengths
Red = longest wavelength & lowest frequency
Violet = shortest wavelength & highest frequency
White light is all colors combined
Three primary colors of light are red, green and blue
How is this different from three primary colors of pigment, from art class?
Read and do pg. 85

4. The Electromagnetic Spectrum!
-All the frequencies (or wavelengths) that an EM wave can have!
Longest wavelength – shortest wavelength /Lowest frequency – highest frequency (p. 86)
Radio waves –
Microwaves –
Infrared light –
Visible light –
Ultraviolet light –
X rays –
Gamma rays -

5. Radiation The sun gives off ALL types of radiation
BUT MOSTLY visible light
What type of radiation are harmful to humans?
Anything with a higher frequency than visible light.
How are we protected from harmful X rays and gamma rays?
The atmosphere!
How do we protect ourselves from UV rays? (the ones that cause skin cancer and eye damage)
Sunscreen, hats, long-sleeved shirts, sunglasses

6. EM Radiation and Energy
High frequency means more energy
What EM waves are safe?
Which ones can cause damage to humans?
More energy means more dangerous!

7. Lesson 2 - The Interactions of Light and Matter
A review: what is matter?
Matter can do three things with light

8. Matter can reflect light – this is how we are able to see the matter!
If something reflects ALL visible light, it looks white
Reflect = light bounces off
Matter can absorb light
If something absorbs ALL visible light, it looks black because we can’t see any of the light reflecting back at us
Absorption = transfer of light energy to matter
Matter can transmit light
(next slide!)

9. Light transmission Matter that transmits light well is transparent
Air, water, glass
all light passes through
Matter that transmits light BUT doesn’t let light travel straight through is translucent
Frosted glass
Matter that doesn’t let light through at all is opaque
Opaque materials absorb light

10. Color
Usually, if something looks a certain color, it’s because that color of light is reflected back to the eye and ALL the other colors are absorbed
Perceived Color can also be affected by…
the color of a translucent object
the color of the available light

11. When Light Goes Through a (Transparent) Medium…
1. It can SLOW DOWN
Light goes the speed of light in a vacuum, BUT when it hits a medium like air or water it slows down
Light travels faster in air than water
Shorter wavelengths are slowed more than longer ones
So violet light is slowed more than red. So red light goes faster than violet (in air)!

12. 2. It can CHANGE DIRECTION
Refraction = the change in direction of water as it passes from one medium to another (show pencil in water)
Waves with short wavelengths refract more than waves with longer wavelengths
So violet bends the MOST
Red bends the LEAST

13. 3. It can SCATTER
Light gets reflected and absorbed by particles (dust, etc)
This is why the sky looks blue!
Short wavelengths (like blue and violet) get scattered more than long wavelengths
As sunlight goes through the air, blue light gets scattered first – this makes the sky look blue to us
When sun is near horizon, sunlight passes through more atmosphere
Then ALL the blue light gets scattered so much we can’t see it, and only longer ones are left
We see this as red, orange and yellow of sunset

14. How to make a periscope

15. How to make a periscope