Week 1 - Intro Quantum I

Question 1

Light is _______

Answer 1

Electromagnetic Radiation

Question 2

As you move from UV to infrared, does wavelength increase or decrease?

Answer 2

Increase

Question 3

(1) What is wavelength, (2) what symbolizes it, and (3) what units is it measured in?

Answer 3

(1) The distance a wave travels in one cycle, (2) λ, and (3) nanometres (nm)

Question 4

(1) what is frequency, (2) what symbolizes it, and (3) what units is it measured in?

Answer 4

(1) The number of cycles a wave undergoes per second, (2) ν, and (3) Hertz (Hz), aka s^-1

Question 5

What is amplitude?

Answer 5

1/2 the height of a wave from peak to trough

Question 6

Relationship between wavelength and frequency?

Answer 6

Inversely proportional

Question 7

How are waves and particles different? (moving from one medium to another)

Answer 7

waves undergo refraction; particles slow down and follow a curved path

Question 8

How are waves and particles different? (interaction with an object)

Answer 8

waves bend around an object, may result in diffraction; particles have a binary response, they are either obstructed or not

Question 9

Interference of waves can be…

Answer 9

constructive or destructive

Question 10

Classical definitions of matter and light could not describe what three major observations?

Answer 10

1. Blackbody Radiation
2. Photoelectric Effect
3. Atomic Spectra
   Attempting to understand these led to the Quantum Theory that describes matter and light as having both particle- and wave-like properties

Question 11

What is a blackbody?

Answer 11

A theoretical (ideal) model that absorbs all radiation falling on it – A “perfect” absorber or emitter. To stay in thermal equilibrium, it must emit radiation at the same rate as it absorbs it so a blackbody also radiates well.

Question 12

What is blackbody radiation?

Answer 12

Everything at a temperature emits radiation with the same shape curve, just ‘shifted’ to shorter wavelength as things get warmer (visible if hot)

Question 13

What is Ultraviolet catastrophe?

Answer 13

(Related to blackbody radiation) the predicted results from classical theory deviated from the observed data, especially at shorter wavelength - showed intensity becoming infinitely large as the wavelengths became smaller

Question 14

What was the theory behind the mathematical expression to describe the phenomenon of blackbody radiation, and what was the expression developed?

Answer 14

Theory: that energy only assumes certain values (is quantized), E = nhv (or E = hv for n=1; Hydrogen). E = energy of the radiation, n = quantization factor (element number), h = Planck’s constant, v = frequency

Question 15

What is photoelectric effect?

Answer 15

When reflecting light off metal surfaces, it was observed that light sources above a threshold frequency could eject electrons from the surface. However, light sources below that threshold would never eject electrons even when the brightness was increased.

Question 16

Why could photoelectric effect not be explained with classical mechanics? What do we know now that we did not back then?

Answer 16

According to classical mechanics, there was no relation between the kinetic energy and the frequency of light. Now, we know that KE increases with frequency.

Question 17

What is the work function (required to remove an electron) dependent on? How is work function represented?

Answer 17

Threshold frequency; work function of metal = Φ

Question 18

How is the kinetic energy of an electron (reflecting off a metal surface) determined?

Answer 18

The excess energy (h*v) over the threshold freq/work function

Question 19

What did einstein discover (related to photoelectric effect)?

Answer 19

Light comes in packets - photons

Question 20

How is velocity represented?

Answer 20

u

Question 21

In the equation (hν = ½mu^2 + hv0), what does each part mean?

Answer 21

h = Planck’s constant
v = frequency
- h*v = Energy of photon
m = mass of electron (constant)
u = velocity
- ½mu^2 = kinetic energy of electron
hv0 = threshold frequency = Φ (work function)

Question 22

Classical vs. observed idea: relationship between frequency of light and kinetic energy of electron

Answer 22

Classical: no relationship
Observed: once threshold is passed, as frequency increases KE increases as well

Question 23

Classical vs. observed idea: relationship between number of electrons and kinetic energy of electron

Answer 23

Classical: as frequency increases, so does number of electrons
Observed: no relationship after threshold passed

Question 24

Graphically, how were Einstein’s explanations of photoelectric effect proved?

Answer 24

JJ Thompson; y-intercept is equal to negative work function

Question 25

Spectra is…

Answer 25

unique to and characteristic of each element (colour lines like we saw in the lab)

Question 26

What was Rutherford’s atomic model and what were the two major problems with it?

Answer 26

Model: nucleus at centre, positively charged, surrounded by electrons
Problems: orbiting electrons should spiral into the nucleus, emission spectrum from such an atom should be continuous
Phenomenon: what keeps the electrons away from the nucleus and the atom stable?

Question 27

In Rydberg’s equation (1/𝜆 = R (( Z^2 / n1^2 ) - ( Z^2 / n2^2 ), what does each term mean?

Answer 27

𝜆 is the wavelength; 1/𝜆 is called the wave number
R is Rydberg’s constant
Z is atomic number (H=1, He=2, Li=3…)
n1 and n2 are positive whole numbers, where n2 > n1. They represent the movement between energy levels.