1. Quantization and Light
Vocabulary:
photoelectric effect
photon
wave
wavelength (λ)
amplitude
frequency (ν)
electromagnetic (e.m.)
spectrum/wave/energy
speed of light (c)
Plank’s constant (h)
Joules (J)
Dan Flavin
Untitled (Marfa Project)

2. Remember?
According to Neils Bohr’s atomic theory, why do elements give a bright-line spectrum rather than a continuous spectrum?

3. Remember?
What is a particle (packet) of light called?

4. Dual Nature of Light

5. Light is a Particle (Photon)
travels in straight lines at great speeds
is reflected from mirrors in a predictable way
Has energy in discrete packets, momentum
Photoelectric effect
Newton observed that the reflection of light from a mirror resembles the rebound of a steel ball from a steel plate

6. Photoelectric Effect

7. Light is a Wave
Thomas Young showed that light is a wave, because it undergoes diffraction and interference (Young’s double-slit experiment)

8. Light is a Wave
Click here for video
Click here for video

9. Properties of Waves
wavelength (λ): the distance from one point on a wave to the next identical point. unit = m

10. Properties of Waves
amplitude: distance from the line of origin to the crest OR the trough. unit = m
amplitude
line of origin

11. Properties of Waves
frequency (ν): number of waves per second that pass a given point. unit = Hz

12. Practice
What is the wavelength (λ), amplitude, and frequency (ν) of the following wave if this segment takes 2 s to pass a given point?
m m m m m m
0m 28c 56cm 84cm

13. λ = 24 m amp = 28 cm ν = 1.5 Hz Practice
What is the wavelength (λ), amplitude, and frequency (ν) of the following wave if this segment takes 2 s to pass a given point?
m m m m m m
0m 28c 56cm 84cm
λ = 24 m
amp = 28 cm
ν = 1.5 Hz

14. Notice that energy and frequency are directly related.
Notice that frequency and wavelength are inversely related.

15. The speed of light (c)* * “light” is a generic term for any electromagnetic wave
The speed at which light travels through air is approximately 300 million meters per second, or c = 3.00x108 m/s.
Light travels almost a million times faster than sound.

16. Speed of Light
The speed of a wave is determine using the following equation:
speed = λ x ν
For all electromagnetic waves, the speed is c. So,
c = λ x ν

17. RADIO WAVES
Have the longest wavelengths and lowest frequencies of all the electromagnetic waves.
A radio picks up radio waves through an antenna and converts it to sound waves.
Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency.
MRI (MAGNETIC RESONACE IMAGING)
Uses Short wave radio waves with a magnet to create an image

18. MRI of the Brain

19. AM=Amplitude modulation—waves bounce off ionosphere can pick up stations from different cities.
(535kHz-1605kHz= vibrate at 535 to 1605 thousand times/second) +

20. FM=Frequency modulation—waves travel in a straight line & through the ionosphere--lose reception when you travel out of range.
(88MHz-108MHz = vibrate at 88million to 108million times/second) +

21. MICROWAVES Used in microwave ovens.
Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food.
Used by cell phones.
RADAR (Radio Detection and Ranging)
Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.

22. Infrared (IR) - “below red”
You can feel the longest ones as warmth on your skin
Heat lamps give off infrared waves.
Thermogram—a picture that shows regions of different temperatures. Temperatures are calculated by the amount of infrared radiation given off.

23. Visible Light The only electromagnetic waves we can see.
ROY G BIV is order from lowest energy to highest energy.
Extremely small portion of the electromagnetic spectrum.
White light contains all colors of visible light.

24. Visible Light as Part of the EM Spectrum
click here for video

25. Ultraviolet (UV) - “above violet”
Shorter wavelength and higher frequency than visible light
Used to kill bacteria. (Sterilization of equipment)
Causes your skin to produce vitamin D (good for teeth and bones)
Too much can cause skin cancer.
Use sun block to protect against UV rays.

26. X-Rays Carry a great amount of energy Can penetrate most matter.
Calcium in bones and teeth absorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed)
Too much exposure can cause cancer
lead vest at dentist protects organs from unnecessary exposure

27. Gamma Rays
Carry the greatest amount of energy of all electromagnetic waves and can penetrate most materials.
Used in radiation treatment in targeted manner to kill cancer cells.
Released in nuclear power plants and by nuclear weapons.
Can be very harmful if not used correctly.

28. EM Energy
The energy of an electromagnetic wave is directly related to its frequency. The energy of one photon of EM energy can be calculated using the following equation:
Ephoton = hν
where h is Plank’s constant which was experimentally determined.
h = 6.626x10-34 J•s
the unit for energy is Joules, J.