1. Sec. 18.1- Electromagnetic Waves

2. Waves- all around us
X-rays, microwaves, ovens, cell phones, wireless internet, heat lamps all use waves in order to travel

3. Without waves, we would not be able to receive energy from the Sun, watch TV, listen to the radio, use wireless internet, use cell phones to call or text… we wouldn’t even be able to see anything!
Many of these waves are actually invisible to us!

4. What are electromagnetic waves?
Electromagnetic waves display some behaviors similar to those of mechanical waves
Even though there are similarities, there are many behaviors that are unique to electromagnetic waves

5. Electromagnetic waves- transverse waves consisting of changing electric fields and changing magnetic fields
Electromagnetic waves carry energy from one place to another (like mechanical waves)- they just carry it differently

6. Electromagnetic waves are produced by constantly changing fields
Electric field- region of space that exerts an electric force on charged particles (ions)
Produced by charged particles and changing magnetic fields

7. Magnetic field- region of space that produces magnetic forces
Produced by magnets, changing electric fields, and vibrating charges
Electromagnetic waves are produced when an electric charge vibrates or accelerates

8. How electromagnetic Waves Travel
Changing electric fields cause magnetic fields to change, and changing magnetic fields cause electric fields to change
Due to this, electric and magnetic fields regenerate each other- cyclic process that repeats itself in a pattern

9. Picture of Electromagnetic Wave:

10. As the electric and magnetic fields regenerate each other, their energy travels in the form of a wave
Electromagnetic waves do not need a medium- they can travel through vacuums
Travel because of the pulsating/changing of the electric and magnetic fields- no matter is required for this to occur

11. Even though they don’t need mediums, electromagnetic waves are still able to travel through any form of matter as well
The transfer of energy by electromagnetic waves is called electromagnetic radiation

12. Electromagnetic Waves- Speed
All electromagnetic waves travel at the same speed through a vacuum- these waves may be slowed down if they travel through matter
Through a vacuum, electromagnetic waves all travel at the speed of light
Speed of light = 3.00 x 108 m/s

13. Electromagnetic Waves- Wavelength and Frequency
Even though electromagnetic waves travel at the same speed, they are not the same- in fact there are a large variety of different types of electromagnetic waves
Electromagnetic waves can have different wavelengths and frequencies

14. Since the speed of an electromagnetic wave is constant (all will be assumed to have the speed of light), wavelength and frequency of the waves are inversely proportional to each other (just like for mechanical waves)

15. We can use the wave speed equation to calculate wavelengths and frequencies of electromagnetic waves
This can further give us information on the type of electromagnetic wave we are dealing with, and how much energy it is carrying

16. Wave speed equation:
A radio station broadcasts a radio wave with a wavelength of 3.0 meters. What is the frequency of the wave?

17. Light acts as both a wave and a particle
Photons
Light acts as both a wave and a particle
In certain situations, we can see the wave behavior of light
In other situations, we can observe how light acts as a particle

18. When light, as well as all electromagnetic radiation, travels, it travels in packets of energy
These packets of energy are called “photons”
Photons will carry different amounts of energy depending on the frequency of the electromagnetic wave

19. Photons containing high frequency electromagnetic waves will carry more energy
So if frequency of an electromagnetic wave increases, its energy also increases and vice versa
Blue light has a higher frequency than red light. If you have a photon of blue light, and a photon of red light, which one will have more energy?

20. Intensity: rate at which a wave’s energy flows through a given area
Intensity is related to the brightness of a light
High intensity light= very bright light

21. What happens at night when you walk further and further away from a street light?
What does this mean about the intensity of light as you increase the distance from the light source?
If you get farther away from a light source, what happens to the distance photons have to travel to get to you?

22. Intensity of light decreases as photons travel farther from the source
The farther the photons have to travel, the more spread out they get- creating light that is not as concentrated/intense
This phenomena can be modeled by a can of spray paint

23. When the can is close to a piece of paper, the paint forms a small, dark spot
When the can is farther away from a piece of paper, the paint forms a large, fainter spot
Same amount of paint spread out over a larger area