2.5 Quantum Physics

Question 1

Define a photon

Answer 1

Indivisible packet of electromagnetic energy

Question 2

Equation for calculating energy in a photon

Answer 2

E = hf

Question 3

Equation for energy in a photon involving wave equation

Answer 3

E = hc/&

Question 4

Use the photon model to explain the photoelectric effect (2 key words)

Answer 4

Photon strikes an electron on a certain energy level. If the energy of the photon is greater than the work function of the metal the electron is freed

Question 5

Equation to find ke of photon ejected

Answer 5

0.5 m v^2 = hf - hf0

Question 6

Equation to find change in energy of photon

Answer 6

hf = deltaE

Question 7

What is the lowest energy level in an atom called

Answer 7

Ground state

Question 8

What is ground state

Answer 8

Lowest possible energy level in an atom

Question 9

What is the term given to an electron that has jumped up an energy level ? Gone down an energy level?

Answer 9

Excitation
De excitation/relaxation

Question 10

Explain laser action (3 key terms) (4)

Answer 10

e are excited to metastable state where they stay for longer time
Population inversion because more e are in excited state compared to lower ( ground ) state
Stimulated emission when e fall
Photon emitted has same energy as the difference between 2 energy levels

Question 11

How are X rays produced

Answer 11

Rapid deceleration of electrons emits photons of X rays
Stimulated emission produces photons of X rays

Question 12

State similarities and differences between CT scans and X rays

Answer 12

Sim: both produce image using x rays

Diff: in CT scans, the x ray tube and detector move in phase. In x rays machines are all stationary
CT allows for organs to be viewed, X rays are just for bones

Question 13

What does CT stand for

Answer 13

Computed tomography

Question 14

Disadvantages of X-rays and CT scans

Answer 14

Radiation dosages can be harmful (especially to pregnant women and children)
CT is more expensive

Question 15

Describe how X-rays are produced ( machine)

Answer 15

High speed e are produced when thermionic emission of a filament happens. They’re accelerated by the pd across filament
e are beamed towards copper anode with tungsten target where they’re rapidly decelerated, producing x rays

Question 16

How is an X-ray tube insulated

Answer 16

Lead shield
Aluminium filter (for lower energy X-rays)

Question 17

Roughly How much energy is lost in the production of X-rays and how is this energy taken care of?

Answer 17

Over 99%
Coolant is circulated through copper block

Question 18

How do you increase the number of X-rays produced
How do you increase penetrating power of X-rays produced

Answer 18

Increase current through filament
Increase pd across filament

Question 19

First 5 + infinity energy levels for hydrogen
And approx spacing

Answer 19

-13.59
-3.4
-1.51
-0.85
-0.54
0

Top 4,5 and infinity close then spacing gets bigger between levels

Question 20

What is an electron volt and what does 1eV = in joules

Answer 20

1 eV is 1 electron accelerated across a pd of 1V
1.6 x 10^-19 J

Question 21

To convert joules to eV what do you do?

Answer 21

Divide by 1.6x10^-19

Question 22

For emission of an e from a metal surface, what must the f be and how soon will it happen

Answer 22

f >f0 (threshold f)
Instantly

Question 23

State 2 conditions required for an e to be emitted from the surface of a metal

Answer 23

Photon needs to hit e
Energy of photon > work function of metal / f>f0

Question 24

What is the mass of an electron (kg)

Answer 24

9.11x 10^-31

Question 25

Electron volt

Answer 25

Energy possessed by an electron which has been accelerated across a pd of 1V

Question 26

Collimated

Answer 26

All parts travel in same direction

Question 27

Metastable state

Answer 27

Energy level which e is stable for several magnitudes of time longer than a normal energy level