Waves, Energy and Bohr
Science 10 review
What is:
-Velocity?
-Acceleration?
-A speed with a direction
-A change in velocity
A Problem with the Planetary Model
Physicists knew that any time a charged particle accelerated, it would emit radiation, and lose energy.
What is the problem then?
Waves, Energy & Light
Light (a form of energy) can be viewed as a wave travelling through space.
The characteristics of the wave determine the properties of the light.
Light
Light can travel at 3.00x108 m/s
That is 300 000 km every second.
That is just short of the distance to the moon.
Metric Prefixes Reminder
G = 109 n = 10-9
M = 106 μ = 10-6
k = 103 m = 10-3
Wavelength of Light
λ → the greek letter lambda (capital=Λ)
λ is the symbol we use to denote wavelength.
The wavelength of visible
light is between 400 nm
and 800 nm.
Frequency of Light.
v → the greek symbol nu (capital → N)
v is the symbol we use to denote frequency.
Frequency is how many cycles the wave completes every second.
The Hertz
The unit for frequency is s-1 or 1/s
This means waves per second.
An alternate name for this is the Hertz (Hz).
Frequency & Wavelength
If you know the frequency or the wavelength of light you can find the other using the formula:
c=λv
where c is the speed of light.
Practice Questions
c=λv
c=3.00x108m/s
If the wavelength of a wave is 131μm, what is the frequency?
If the frequency of a wave is 148 s-1, what is the wavelength?
Answers
1: 131μm needs to be in m.
v=c/λ=(3.00x108m/s)/(1.31x10-4m)=2.29x1012s-1
2: λ=c/v=(3.00x108m/s)/(148s-1)=2.03x106m
or 2.03Mm
Waves and Energy
The energy that a wave has is proportional to the wave’s frequency (v).
E = hv
h → Planck’s constant = 6.626x10-34 Js
Practice Questions
If the wavelength of yellow light is 580 nm, how much energy does it have?
v=c/λ=(3.00x108m/s)/(5.8x10-7m)=5.2x1014s-1
E=hv=(6.626x10-34)(5.17x1014)=3.4x10-19J
Practice Questions
If the wavelength of red light is 680 nm, how much energy does it have?
v=c/λ=(3.00x108m/s)/(6.8x10-7m)=4.4x1014s-1
E=hv=(6.626x10-34)(4.4x1014)=2.9x10-19J
What did Bohr see?
Niels Bohr
Bohr proposed that electrons exist in unique energy levels.
When an electron moves from one to another, they would absorb or emit light of a specific wavelength.
Quantum Leaps
Electron can jump between levels
Each level has a specific energy level.
Recap and review
How much energy does a wave have if the frequency is 1.83x1014s-1?
How many protons, neutrons and electrons does 202Hg have? and 52Cr?
Recap & Review
What is the wavelength of a wave that has an energy of E= 2.50x10-17J?
If an element has two isotopes with mass numbers 116(33.0%), 117(34.0%), 118(26.0%), and 120 (7.0%), what is the atomic mass?
Homework
Questions 1-10 on the homework. I will be collecting it.
Exit Slip
Please write down on a sheet of paper:
-Your name.
-What is the relationship between the emission spectrum of Hydrogen and the Bohr model of the atom?