Photons and Quantum Physics

Question 1

Energy equation

Answer 1

Planck constant (H) x frequency

Question 2

Speed equation

Answer 2

c=F x Lambda
=frequency X wavelength

Question 3

Work done

Answer 3

Q x V
q= charge of an electron

Question 4

Electron volt

Answer 4

The unit of energy equal to the work done when an electron is moved through a potential difference of 1 volt

Question 5

J->eV

Answer 5

/1.6x10^-19

Question 6

eV->J

Answer 6

x1.6x10^-19

Question 7

Equation of charge when electron free to move

Answer 7

qV=1/2mv^2

Question 8

Equation of electron when electron free to move

Answer 8

eV=1/2mv^2

Question 9

The photoelectric effect

Answer 9

Electrons can escape from the surface of certain metals if the surface of the metal is illuminated by radiation of sufficient frequency

Question 10

Describe what happens in the photoelectric demonstration

Answer 10

The zinc is negatively charged and so the gold leaf is repelled by the metal plate as it is also negatively charged.
The negatively charged gold leaf is attracted to the positively charged UV rays meaning it returns back to normal
This is due to the electrons escaping the zinc when UV light is shone on it

Question 11

The Laws of photoelectric emission

Answer 11

The number of electrons released from the surface is proportional to the intensity of the incident radiation, photo electrons per second are directly proportional to the intensity of radiation
Emission occurs with no observable time lag
The kinetic energy of the photo electrons depends only on the frequency of the light and NOT on the intensity of the light, KEmax proportional to frequency
There exists a threshold frequency f0 of emission when f<f0 no photo electrons are emitted. f0 depends upon the type of metal.

Question 12

What is the name for the certain amount of energy electrons need to be released from the potential energy well?

Answer 12

Work function

Question 13

Work function equation

Answer 13

=hf0

Question 14

Explain the photocell experiment

Answer 14

Light is allowed to hit a photo-emissive surface. The photo electrons electrons cross the evacuated tube and go to eatch via the ammeter. The current therefore measures the amount of photo electrons emitted by the photo cathode.
The potential of the collector plate can be made more positive or negative relative to the emitting surface
the collector plate is made more negative in order to repel the electrons thus creating a potential hill

Question 15

KE max equation in photocell

Answer 15

KEmax=eVs
Vs= kinetic energy of the electrons

Question 16

Ke/frequency graph

Answer 16

Gradient=planks constant
X-intercept=f0-frequency threshold-frequency when KE=0
Y intercept=work function

Question 17

different metal for KE/frequency graph

Answer 17

gradient stays the same but work function would change and so would the threshold frequency

Question 18

different light intensity for KE/frequency graph

Answer 18

wouldn’t affect graph

Question 19

Significance of the photocell experiment

Answer 19

proves that em spectrum waves are quantifed into particles of energy, proves the particle nature of lights + validates planks constant

Question 20

Electron diffraction experiment

Answer 20

Electrons evaporated off a heated cathode are accelerated towards a thin carbon target
The electrons are abler to pass through the carbon and hit a screen to give a pattern. The spacing between the carbon atoms behaves like a diffraction grating.
The existence of electron diffraction provides evidence that electrons behave like waves.

Question 21

Radiation pressure equation

Answer 21

Momentum change per second/area of beam

Question 22

Absorption spectra

Answer 22

Obtained by passing continous spectra through a cold gas, electrons jump up energy level

Question 23

Emission spectra

Answer 23

Obtained by heating a gas so that it emits light,electron jumps down energy level and give off a photon, the electrons need less energy as they are closer to the nucleus

Question 24

Photon energy equation

Answer 24

hf=E1-E2