Quantum Physics

Question 1

Photon

Answer 1

A photo is a massless packet of discreet quantity of electromagnetic energy.

Question 2

Photon energy equation

Answer 2

E=hf E=hc/wavelength

Question 3

Photon momentum

Answer 3

P=E/c

Question 4

Define electronvolt

Answer 4

The energy gained by an electron travelling through a potential difference of 1 volt

Question 5

What is the relation of electron volt to kinetic energy

Answer 5

ev=1/2mv^2

Question 6

Convert from ev to j

Answer 6

Multiply by 1.6x10^-19

Question 7

What is the photoelectric effect

Answer 7

Is the phenomenon in which electrons are emitted from the surface of a metal upon the absorption of electromagnetic radiation
The electrons removed are called photoelectrons

Question 8

How does the photoelectric effect provide evidence that light is quantized

Answer 8

Each electron can only absorb a single photon
This means only frequencies of light above a threshold frequency will emit a photoelectron

Question 9

Describe the photoelectric effect using the gold leaf electroscope

Answer 9

A plate of metal is attached to a gold leaf, which initially has a negative charge, causing it to be repelled by a central negatively charged rod. This causes a negative charge
Uv light is shone onto the metal plate, leading to the emission of photoelectron
Less negative charge so gold leaf falls

Question 10

What would happen by placing the uv light closer to metal plate

Answer 10

Gold leaf will fall more quickly
As intensity incidents increase
This increases the number of photo electrons emitted per second

Question 11

What would happen by using a higher frequency on gold leaf

Answer 11

Doesn’t change how quick gold leaf falls
Ke Inc with frequency but freq and ke are both independent of intensity

Question 12

What would happen by using a filament lamp yo the gold leaf

Answer 12

No change in gold leaf position
Incident freq below threshold freq

Question 13

Threshold frequency

Answer 13

The minimum frequency of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal

Question 14

Threshold wavelength

Answer 14

Longest wavelength of incident electromagnetic radiation that would remove a photoelectron from the surface of a metal

Question 15

Photoelectric equation

Answer 15

Threshold energy + ke of photoelectron

E=hf= threshold energy +1/2mv^2max

Question 16

Threshold energy

Answer 16

The minimum energy required to release a photoelectron from the surface of a metal

Question 17

What is wrong in wave theory

Answer 17

1) any freq of light can give rise to photoelectric emission if the exposure is long enough
2) the energy absorbes by each electron increases gradually with each wave
3) ke of emitted electrons should increase with radiation intensity

Question 18

How do waves show wave particle duality

Answer 18

By diffraction

Question 19

If there is a low accelerating voltage, what happens to the radius of diffraction rings

Answer 19

Increases

Question 20

If there is a high accelerating voltage, what happens to the radius of diffraction rings

Answer 20

Decreases

Question 21

De brogli wavelength

Answer 21

The wavelength associated with a moving particle

Question 22

De brogli wavelength equation

Answer 22

Wavelength=h/p
Wavelength= h/mv
E=1/2mv^2
So E=p^2/2m p=squareroot(2mE)
Wavelength= h/squareroot(2mE)

Question 23

What are the 2 types of spectra

Answer 23

Emission
Absorption

Question 24

Emission spectra

Answer 24

Emission of a photon
(Dark with colored lines)

Question 25

Absorption spectra

Answer 25

Absorb a photon
(Coloured dark line)

Question 26

Calculating discrete energy levels

Answer 26

^E = hf = E2-E1
Wavelength=hc/(E2-E1)

Question 27

What provides evidence to show electrons in atoms can only transition between discrete energy levels

Answer 27

The line spectrum in not continuous but rather contains only discrete values of wavelength