1. Electromagnetic Radiation
Unit 4, Section B

2. The Electromagnetic Spectrum
Light is electromagnetic radiation (energy that exhibits wavelike behavior).
Electromagnetic spectrum: Radio, Microwave, Infrared, Visible, Ultraviolet, X-Ray, Gamma Ray (long wavelength to short wavelength)

3. The Electromagnetic Spectrum3

4. Types of Electromagnetic Radiation
Radio Waves: longest wavelengths = lowest frequencies
Used for wireless transmission of sound messages and other information
Very High Frequency (VHF) – FM radio and TV
Super Low Frequency (SLF) – communicate with submarines underwater
Also, emitted by stars and gases in space and studied by astronomers to gather information about the universe.

5. Types of Electromagnetic Radiation (cont’d)
Microwaves: between radio waves and infrared radiation
Used for heating and cooking food
Carry telephone and TV signals between stations on Earth and communication satellites
Used in radar systems to track position and speed of various objects

6. Types of Electromagnetic Radiation (cont’d)
Infrared Radiation: between microwaves and visible radiation
aka Heat - invisible to naked eye but detected as warmth by the skin
Used in night vision instruments, meteorology, telecommunications

7. Types of Electromagnetic Radiation (cont’d)
Visible Radiation: red borders infrared and violet borders ultraviolet
aka Light – visible to human eye and consists of a continuous spectrum of colors: ROYGBIV
Visible radiation is emitted by everything from fireflies to light bulbs to stars
½ of Sun’s energy is released as visible radiation
Essential for photosynthesis

8. Types of Electromagnetic Radiation (cont’d)
Ultraviolet (UV) radiation: between visible radiation and x-rays
Sun is a source of UV radiation – UV rays burn/tan our skin
Over-exposure results in skin cancer, eye cataracts, and damage to body’s immune system
Ozone layer naturally protects against the most harmful UV radiation emitted by the Sun

9. Types of Electromagnetic Radiation (cont’d)
X-Rays: between UV radiation and Gamma Rays
Used to generate images of the human body (bones, tissue, and teeth)
Over-exposure can cause cancer and birth defects
Hot gases in the universe emit X-rays

10. Types of Electromagnetic Radiation (cont’d)
Gamma Rays: shortest wavelengths = highest frequencies
Used to sterilize medical instruments and supplies which cannot be boiled
Damages biological organisms by penetrating substances deeply
Radioactive materials emit gamma rays
Radon gas emits gamma rays
Greatest generator is the Universe

11. Solar Radiation
Most of the radiant energy emitted by the Sun is spread over a large portion of the electromagnetic spectrum:
45% is in the infrared (IR) region
46% is in the visible region
9% is in the ultraviolet (UV) region
Less than 1% of solar radiation falls outside of these three regions

12. Properties of Light
Speed of Light = Constant speed (c) of 3.0 x 108 m/s through a vacuum.
Light consists of waves
Wavelength ()
Crest to crest
Trough to trough
Between two identical points
Frequency ()
# of waves that pass a given point in an assigned time
Usually 1 second
Hertz (Hz) = waves/second

13. Properties of Light (cont’d)
Wavelength and frequency
Inversely proportional
Wavelength increases, frequency decreases
c = λ ν
Note: c= speed of light, λ=wavelength, v=frequency

14. Practice Problem #1
A certain green light has a frequency of 6.26x1010 Hz. The speed of light is 3.00 x 108 m/s. What is the wavelength?
c = λ v
Hz = 1/s
λ = c/v = 3.00x108 m/s
6.26x1010 Hz
= 4.79 x10-3 m

15. Practice Problem #2
Violet light has a wavelength of 4.10x10-7 m. The speed of light is 3.00 x 108 m/s. What is the frequency of the light?
λ = 4.10x10-7 m
c = 3.00 x 108 m/s
v = ?
C = λ ν
v = c / λ = 3.00x108m/s
4.10x10-7 m
= 7.32x1014 1/s or Hz