1. Light and The Electromagnetic Spectrum
Unit 10

3. Electromagnetic Waves
transverse waves consisting of alternating electric and magnetic fields.
produced when an electric charge vibrates
Can travel through a vacuum
Vacuum: empty space, no air or medium
Does not require a medium
Travel at the speed of light (c)
v= 3 x 108 m/s = c

4. EM Spectrum – Relationship between frequency, energy and wavelength
long 
low f
low energy
short 
high f
high energy

5. Relationships EM Waves High frequency = short wavelength = high energy
Low frequency = long wavelength = low energy
Sound
Greater amplitude = higher energy

6. Electromagnetic Spectrum
What are the numbers on the electromagnetic spectrum?
Wavelengths are given on the EM Spectrum. If you know the wavelength, you can find the type of EM wave…

7. What type (or color) of EM wave is it?
λ = 4.3 x 10-2 m: ___Microwave_
λ = 8 x m: ___X-rays____
λ = 6.1 x 10-7 m: __Orange____
λ = 4.8 x 10-4 m: ___Infrared___
f = 6 x 104 Hz: __Radio waves_

8. Look at the size comparison of the wavelengths!!

9. Radio Waves Include AM, FM and Television frequencies
Longest wavelengths & lowest frequency of the EMS
Include AM, FM and Television frequencies
AM – Amplitude modulation: the frequency stays the same, but there is a change in the amplitude to get different sounds etc.(travel further than FM)
FM – Frequency Modulation: slight changes in frequency

10. RADAR Stands for Radio Detection and Ranging
Uses a radio transmitter to send out short bursts of radio waves
Waves reflect off objects they encounter and bounce back towards where they came from (the radio receiver) and are interpreted
We use this to see WEATHER in the clouds!

11. Microwave & Infrared
Microwave: used in microwave ovens & cellular phones
Infrared: Fast Food Heat Lamps, use as a night time surveillance tool.

12. Visible Light
White light is a mixture of the entire visible light spectrum
Small part of the spectrum that we can see.
ROY G. BIV. Color in order of increasing energy.

14. UV, Xray & Gamma rays
UV from the Sun helps the body produce vitamin D, too much exposure can cause skin cancer
Xrays: used extensively in medicine to see “into” the body
Gamma Rays: used in medicine to treat cancer or destructive radiation from nuclear explosions.

15. Wave Energy & Health Risk
LOW ENERGY
Radio Waves: AM/FM
Microwaves: Microwave ovens, Cell phones
Infrared: Warm objects, Night vison goggles
Visible Light: Red  Violet
Ultraviolet: Sunburns, skin cancer
X-Rays: Goes through skin, reflected by bone
Gamma Rays: Causes cancer; Used in radiation therapy to kill cancer cells; given off by nuclear reactions
HIGH ENERGY

16. Review

17. Light and Matter Opaque Transparent Translucent
absorbs or reflects all light
Transparent
allows light to pass through completely
Translucent
allows some light to pass through

18. Stimulates red & green cones
Seeing Colors
The retina contains…
Rods - dim light, black & white
Cones - color
red - absorb red & yellow
green - absorb yellow & green
blue - absorb blue & violet
Stimulates red & green cones
Stimulates all cones

20. Seeing Colors Color Blindness
one or more sets of cones does not function properly
If you are not colorblind, you will see 57. If you are colorblind, you will see 35.

21. Mixing Colors EX: computer RGBs Primary light colors red, green, blue
additive colors
combine to form white light
EX: computer RGBs

22. Mixing Colors
Filter
transparent material that absorbs all light colors except the filter color

23. Mixing Colors EX: color ink cartridges Pigment Primary pigment colors
colored material that absorbs and reflects different colors
Primary pigment colors
cyan, magenta, yellow
subtractive colors
combine to form black
EX: color ink cartridges

25. Negative Afterimage - One set of cones gets tired, and the remaining cones produce an image in the complimentary color.

26. Light Applications

27. Speed of Light
All light travels through a vacuum (empty space) at a speed of 3 x 108 m/s!
How are different types of light different from each other?
Different Wavelengths/Frequencies

28. Velocity of Sound vs. Light
Sound through air at room temp (20oC/68oF)
= 343 m/s
Light
Electromagnetic wave in a vacuum = 3 x 108 m/s
This is why you see lightning before you hear thunder!

29. Speed of Light
Light travels fastest through a vacuum, slows down in liquids and solids.
When light moves into a denser medium, it slows down and BENDS!  Refraction

30. Refraction of Light - Prisms

31. Refraction of Light - Lenses
A magnifying glass can be used to start a fire.
Eyeglasses (Corrective lenses)
Mirages

32. Concave & Convex Mirrors

33. Review – What type of wave?

34. Review solid What wavelength(s) are being reflected? vacuum
What medium does sound travel fastest through: solid, liquid, gas, or vacuum?
What medium does light travel fastest through: solid, liquid, gas, or vacuum?
If you see an apple as red…
What wavelength(s) are being reflected?
What wavelength(s) are being absorbed?
solid
vacuum
red
All other colors

35. Review The pitch of a sound is determined by the wave’s ____________.
The loudness of a sound is determined by the wave’s ____________.
The higher the energy of a light wave, the greater its ____________.
frequency
amplitude
frequency