1. Electromagnetic Waves & The Electromagnetic Spectrum
S8P4 a
S8P4 d

2. Waves Most electromagnetic waves are invisible
Detect the present of waves by what we can see, feel, or hear

3. Electromagnetic Waves
Electromagnetic waves are a disturbance that transfers energy through a field
You have a EM wave when the disturbance occurs in a electric or magnetic field rather than in a medium

4. Sources
The Sun is main source of EM waves and provides most of the energy for Earth!
Stars also can give off EM waves but their wave don’t always make it to earth because of the distance between the earth and stars
Humans use technology to give off EM waves

5. How they travel
Energy that moves in the form of EM waves is called radiation
Mechanical waves must have a medium whereas EM waves can travel without a medium-like in a vacuum
EM waves do not lose energy as they move so they can travel forever!

6. Vacuum
Sun waves travel ~150 million km to reach earth (93 million miles)
Rays from other galaxies can travel billions of years before reaching earth
Waves in a vacuum spread out and travel until something interferes
The further they travel, the more they will spread and the less waves in a area (which means less energy being transferred to the area in which the wave will encounter)

7. Speed Travel at a constant speed and very fast (300,000 km per second)
Sun rays take 8 minutes to reach Earth
This constant speed is called the speed of light

8. EM Waves and mediums
When EM waves encounters a medium, it will react with it just like a mechanical wave…they transfer energy to the medium
They will also reflect, refract, or diffract which causes the energy to change direction

9. Answer the following questions:
How are EM waves different from mechanical waves?
What are two sources of EM waves in Earth’s environment?
How can EM waves transfer energy differently in a material medium as compared to a vacuum?
What might be one cause of uneven heating in a microwave oven?

10. The Electromagnetic Spectrum
S8P4a

11. Electromagnetic Waves
Electromagnetic waves come in many wavelengths and frequencies. Each one is useful in different ways.

12. Electromagnetic Spectrum
The electromagnetic spectrum is the range of all EM frequencies
The EM spectrum is a smooth, gradual progression from the lowest frequencies to the highest (and wavelengths)

14. Radio Waves
Waves that have the longest wavelength, the lowest frequency, and lowest energy
Travel easily through the atmosphere and materials
Radio waves are broadcasted by a transmitter where a receiver picks up the signals and converts it to sound waves
Radio stations use different frequencies so they don’t get crossed

15. Radio Waves
Two ways to modulate radio wave is by changing the amplitude and varying the frequency
Amplitude is used for AM
Frequency is used for FM
Televisions also use radio waves…they use AM signals for the picture and FM for the sound

16. Microwaves
Have shorter wavelengths, higher frequencies, and higher energy than other radio waves
Important uses of microwaves are radars and cell phones
Radars (WWII) transmits microwaves, receives reflections, and converts it into visual images
Radar led to the invention of the microwave oven

17. Microwaves
Your cell phone is actually a radio transmitter and receiver that uses microwaves
Sends and receives signals from a tower and is where the signals come together and allow you to connect with other person

18. Infrared Light
Found between microwaves and visible light, is the type of EM waves most often associated with heat
You cannot see infrared light, but you can feel the results
Examples: Warming lights at restaurants and your toaster

19. Visible Light
Part of the EM spectrum that humans can see and is the smallest part of the spectrum
The longest wavelength is “red” and the shortest is “violet”
The visible light from the sun is white light (all wavelengths are combined)

20. Visible Light
The range of colors is called the visible spectrum

21. Visible Light used in many ways
Vision
Find food and other survival activities
Plants need it to make their food
Can you think of anything else?

22. Where does it come from? Most of it comes from the sun
The production of light by materials at high temperatures is called incandescence
Other sources include: Lightening and Fire

23. Living things produce light
Luminescence is the production of light without the high temperatures needed for incandescence.
The production of light by living organisms is called bioluminescence.
Produce by chemical reactions and not intense heat
Insects, worms, fish, squid, jellyfish, bacteria, and fungi

24. Human produced visible light
First was fire
Electrical lighting in late 1800’s (used tungsten) was known as incandescent bulbs
Fluorescence bulbs
Use gas instead of a filament
Neon lights (diff gases produce diff colors)
LED’s uses a semiconductor that regulates electric current to produce light

25. LED’s Light-emitting diodes
Idea came from the bioluminescence of animals
Light that produces little heat and uses almost all of its electrical energy to make light instead of the thermal energy
Not easily broken

26. Ultraviolet Light (radiation)
Has frequencies above those of visible light and partially below those of x-rays
Carries more energy than visible light
Waves can damage skin and eyes (cause sunburn)
Used to: sterilize medical equipment, kill harmful bacteria, produce vitamin D, treat skin problems and other medical conditions

27. X-rays Very high frequencies and energy Produced by sun and stars
Pass through soft tissue but is absorbed in dense matter, like bones
Over exposure to x-rays can cause cancer
Lead can block these types of EM waves

28. Gamma Rays Highest frequencies and energy of all the EM waves
Produced by sun and stars and some radioactive substances
Gamma rays kill normal cells and cause cancer cells to develop
However, doctors can use gamma rays to kill cancer cells and fight tumors when carefully controlled

30. Short Story For homework:
Write a short story in which the characters use or are affected by each of the different kinds of EM waves
Complete on a separate sheet of paper because you will turn it in