A-LEVEL PHYSICS: 2.4.2: Threshold Frequency & Work Function (SaveMyExams)

Question 1

photoelectric effect:

Answer 1

phenomenon where metal absorbs electromagnetic radiation & electrons are emitted from the surface

Question 2

photoelectrons:

Answer 2

electrons removed from a metal due to the photoelectric effect

Question 3

the photoelectric effect provides evidence that light behaves as a…
why?

Answer 3

particle
bc light is quantised in discrete packets

Question 4

light is quantised in discrete packets. this is shown by:

Answer 4

how each electron can only absorb a single photon

Question 5

only the frequencies of light above a ______ will emit a photoelectron

Answer 5

threshold frequency

Question 6

threshold frequency:

Answer 6

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

min freq of incident EM radition needed to initiate photoelectric effect

Question 7

threshold wavelength:

Answer 7

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

longest wavelength of incident EM radiation that would initiate photoelectric effect

Question 8

wave speed = …

Answer 8

v=fλ

Question 9

since photons are particles of light:

Answer 9

v=c
(speed of photon = speed of light)

Question 10

work function Φ (threshold energy):

Answer 10

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

min energy required to initiate photoelectric effect

Question 11

alkali metals have threshold frequencies in the…
why?

Answer 11

visible light region
bc attractive forces between surface e- & + metal ions are weak

Question 12

transition metals have threshold frequencies in the…
why?

Answer 12

ultraviolet region
bc attractive forces between surface e- & + metal ions are strong

Question 13

stopping potential Vs:

Answer 13

pd required to stop photoelectric effect.
stops e- from flowing from emitter plate to collector plate

Question 14

emitter plate:

Answer 14

photons arriving at the metal plate cause photoelectrons to be emitted

Question 15

collector plate:

Answer 15

electrons that cross the gap at the other metal plate

Question 16

photoelectric current:

Answer 16

flow of e- from emitter plate to collector plate

Question 17

if the emf of the variable power supply is initially 0, the circuit operates only on…

Answer 17

photoelectric current

Question 18

as the supply is turned up, the emitter plate becomes more ___.
as a result:
why:

Answer 18

positive
e- leaving the emitter plate are attracted back towards it
bc the pd across the tube opposes the motion of e- between plates

Question 19

increasing the intensity of the incident radiation on the plate increases: (2)

Answer 19

-number of photons incident on the metal plate

-number of photoelectrons from emitter plate (photoelectric current)

Question 20

for a given potential difference, increasing the intensity increases the ______, but the stopping pd remains the same.
this shows:

Answer 20

photoelectric current
intensity does not affect the Ek of photoelectrons

Question 21

maximum Ek of photons (& photoelectrons) depends on: (2)

Answer 21

-frequency of incident photons
-work function of the metal

Question 22

if the freq/wavelength is changed whilst keeping the intensity constant, the photoelectric current will…

Answer 22

not be constant

Question 23

increasing the freq of a source means:

Answer 23

energy of each photon increases

Question 24

keeping intensity the same means:

Answer 24

energy transferred per unit area in a given time is constant