1. Light and Quantized Energy
Essential Question:
How would you use the formula c=lv and E=hv in wave calculations?

2. Wave Nature of Light?
As we discussed, electrons release energy in the form of a photon. Photons travel in the form of a wave, so it is necessary to understand the functionality of a wave to better understand light.

3. Parts of a wave
peak
wavelength
amplitude
trough

4. Characteristics of Waves
Wavelength ( λ ) – shortest distance between 2 equivalent points on a continuous waves (from crest to crest or from trough to trough)
Units of wavelength:
Usually in meters (100),
Centimeters (10-2) or
Nanometers (10-9)

5. Comparing Wavelengths
Which wave has a longer wavelength?
Which wave has the shorter wavelength?
long wavelength
crest
Wavelength
Wavelength
trough
short wavelength

6. Characteristics of Waves
Frequency ( v ) – number of waves that pass a given point per second
Units of frequency:
waves per second
1 / s = s -1 = Hertz

7. So which type of wave has a higher frequency……one with a long wave length or one with a short wavelength
Wave A
Wave B
Wave C

8. Another way to look at Frequency
These 2 waves are traveling at = speeds…
more crests cross the ‘finish line’ in a matter of one min.?
which wave will have
low frequency
= long wavelength
high frequency
= short wavelength

9. Characteristics of a Wave
Amplitude – wave’s height from the origin of the wave to the crest or from the origin to the trough
origin

10. Vocab & Symbols Speed of light (c) – constant number, 3.00 x 108 m/s
Wavelength ( λ ) – shortest distance between 2 equivalent points on a continuous waves; measured in m
Frequency ( v ) – number of waves that pass a given point per second; measured in Hz
Energy (E) – energy of the photon as it travel; measured in Joules, J
Planck’s Constant (h) – constant number, x J . s

11. Wave Calculations
All electromagnetic waves travel at the speed of light in a vacuum
Speed of light (c) = 3.00 x 108 m/s
Speed of light is equal to product of wavelength and frequency
c = λ v
Rearrange to solve for wavelength or frequency.
Remember speed of light (c) is a constant, always the same number

12. Wave Calculations Practice
Green light has a frequency of 6.01 x 1014 Hz. What is the wavelength?
Violet has a wavelength of 410 nm. What is the frequency?

13. What units of wavelength are needed?
What do you have to do if you are given a wavelength of nm?

14. Photoelectric Effect
Electrons are emitted from a metal’s surface when light with a certain frequency hits the surface

15. Photoelectric Effect
Frequency and energy do not accumulate on the metal’s surface
Specific threshold needed to be reached before the electron would be emitted

16. Dual Nature of Light
Explains the photoelectric effect
Albert Einstein proposed that light has wavelike and particle like properties
Photon – massless particle that carries a quantum of energy
Ephoton = hv

17. Energy Calculations
All energy is a multiple of Planck’s Constant, a quantum of action in quantum mechanics
h = x J . s
Quantum – minimum amount of energy that can be gained or lost by an atom
Planck stated that there was a relationship between the energy of a quantum and the frequency of the radiation

19. E = h v Energy Calculations
Energy of a photon is calculated by the multiple of Planck’s constant by frequency
E = h v
Rearrange to solve for energy or frequency.
Remember Planck’s constant (h) is always the same number

20. Energy Calculations Practice
Calculate the E of a photon of radiation with a frequency of 8.5 x 1014 Hz .
What is the υ of of a wave carrying 8.35 x J of energy?

21. Using BOTH Formulas
What is the wavelength of the yellow sodium emission which has a frequency of 5.09 x 1014 s-1?
The frequency of the strong red line in the spectrum of potassium is 3.91 x 1014 s-1. What is the wavelength of light?

22. Heisenberg Uncertainty Principle
States it is impossible to know the velocity and the position of a particle at the same time.
This is due to the fact that in order to determine the original location of an electron it would have to be hit with a high energy photon to “move” it to the new location, and therefore determine original location.
However, by “hitting” it with the high energy particle would cause the original energy & wavelength to change, so the data would not be accurate.