1. Light
Physics Mrs. Coyle

2. Light is a wave Light shows properties of waves:
Diffraction patterns observed

3. Light is a Particle
Light can travel through the vacuum of space, but mechanical waves can’t travel in a vacuum.

4. So which is it?

5. Electromagnetic Waves: oscillating electric and magnetic fields.

6. Electromagnetic Waves
Do not require a medium.
Can travel through space (vacuum). Ex.: Light from the sun reaches us.
Transverse

7. Electromagnetic Waves
Type of radiation Wavelengths(m)
Radio TV
Microwave
Infrared radiation
Visible Light 700x x10-9
Ultraviolet
X-rays
Gamma rays shorter than 10-12

8. Visible Light is detected by the human eye.
red 700 x (700nm)
orange
yellow
green 550 x 10-9
blue
indigo
violet 400 x (400nm)

9. Electromagnetic Spectrum

11. Speed of Light, c
All EM waves have a speed through vacuum of 3 x 108 m/sec.
c= f λ

12. Problem
If a light wave’s frequency is 5.45 x10 14 Hz, what is its wavelength?
What color light is it?
Answer: 550x 10-9 m, green

13. Calculating the Speed of Light
Danish Astronomer, Ole Roemer (~1668) found that the period of the moon of Jupiter , Io, varied depending on the location of the Earth. Distances were known.
Estimated speed
of light:
2.2 x108 m/s

14. Albert Michelson, American (1880’s)
Measured time for light to make a round trip in California mountains 35km apart.
Measured speed of light:
x108 m/s
First American to win Nobel prize.