unit 2 quantum physics

Question 1

photoelectric effect / emission

Answer 1

emission of electrons from a surface when illuminated with electromagnetic radiation of sufficient frequency

Question 2

1. photoelectric effect / emission

electrons emitted have a range of values of kinetic energies up to a maximum value

why?

Answer 2

1. maximum corresponds to electron emitted from the surface
2. maximum kinetic energy of the electron is the photon energy which is work function
   ( since photon energy is constant, work function is the min energy required to release electron, KE max )
3. electron released from surface
   photon energy = work function
4. electron released below surface
   energy is needed to be brought up to the surface before being released. kinetic energy lower

Question 3

1. photoelectric effect / emission

observations that support the particle theory / photon model but not wave theory

Answer 3

1. existence of threshold frequency
2. photocurrent ( rate of emission of electron ) proportional to intensity
3. max KE of photoelectrons determined by frequency of radiation but not intensity
4. instantaneous emission of photoelectrons

Question 4

threshold frequency

?

Answer 4

f0

the frequency below which no photoelectrons are emitted
or
the minimum frequency of electromagnetic radiation so electron can be emitted from metal surface

Question 5

A ~ particle theory / photon model of electromagnetic radiation

features

first 2

Answer 5

1. electromagnetic radiation makes up of photons
2. photon energy, E proportional to frequency, f
   - 2 formulas on pg
   - first, E=hf , h = planck constant = 6.63 times 10 ^- 34 Js

Question 6

A~ particle theory / photon model of electromagnetic radiation

features

last 3

Answer 6

3. one photon gives all the energy to one electron
4. intensity proportional to the number of photons N per unit time t per unit cross sectional area A
   - power formula pg 1
5. energy of photon independent of light intensity. higher intensity of electromagnetic rad in given frequency means more photons per unit time per unit area

Question 7

photon

Answer 7

quantum energy of electromagnetic radiation

photon energy proportional to frequency

E = hf

Question 8

quantum

Answer 8

very small energy

Question 9

why uv photon has higher energy compare to infra red photon

Answer 9

frequency of uv is higher than infra red photon

but if both have same intensity, number of UV photon per unit time is lower

Question 10

A~

B~ wave model of electromagnetic radiation

Answer 10

1. wave energy depends on intensity
2. energy supplied is continuous and energy can build up and spread over whole wave
3. if given enough time, electron can accumulate enough energy and leave the surface

Question 11

why observation support particle theory not wave theory

FIRST

Answer 11

A~ THE EXISTENCE OF THRESHOLD FREQUENCY

1. electromagnetic radiation makes up of photons
2. photon energy, E proportional to frequency, f
   - 2 formulas on pg
   - first, E=hf , h = planck constant = 6.63 times 10 ^- 34 Js
3. one photon gives all the energy to one electron
4. if photon energy higher than work function then electrons release from metal surface

wave theory : no relationship btwn energy of wave with frequency . electron should emit at all the frequency if metal is illuminated with electromagnetic radiation for long time intervals

Question 12

why observation support particle theory not wave theory

SECOND

Answer 12

PHOTOCURRENT PROPORTIONAL TO INTENSITY

1. electromagnetic radiation consists of photon