Yr 12 - Quantum Physics Flashcards
What is a photon?
Discrete packet of energy
What is the rest mass for a photon at the speed of light?
0
What is a LED?
Diode
What is the threshold voltage?
Max PD of a circuit before any current flows
What is an electron volt?
Amount of KE gained by electron that is accelerated through a PD of 1V
How do you convert from Joules to electon-volts and vice versa?
1ev = 1.6x10^-19 J
Define each letter of the equation
hf = ɸ + KEmax
h = planks constant
f = frequency
ɸ = work function (J)
KEmax = KE of photoelectrons
hf = energy (J)
Describe the Photoelectric effect (experiment)
6 Marks
- EM waves exist as quantas of energy (discrete packets) called photons
- When an EM wave hits metal surface photons are absorbed why electrons 1:1
- Photoelectrons emitted if energy > ɸ
- KE of Photoelectrons depends of energy of photon
- KEmax = Energy of photon - work function
- Number of electrons emitted depends on intensity of EM waves as higher intensity means more photons of light and therefore more photoelectrons emitted.
(Gold leaf, Zinc plate, negative charges)
Describe the setup & effect of the gold leaf experiment
Zinc plate with gold leaf attached
- Zinc plate negatively charged
- Gold leaf falls when EM radiation exceeds (threshold frequency/work function) as electron charges are ejected
- Leaf is upright because it is negatively charged and is repelling the negative charges of the zinc plate.
What does ‘Irradiated’ mean?
Exposed to radiation
In terms of the work function, when does:
- Ek = 0
- Ek > 0
- When E = ɸ
- When E > ɸ
Do photoelectrons have a constant speed?
No, it varies and is not constant
How does Intensity affect frequency/energy?
Intensity has no effect on frequency or energy.
What is the threshold frequency?
Minimum frequency of em radiation causing the emission of an electron from surface of a metal.
What is the work function?
Minimum energy to remove a single electron from the surface of a metal.
Define each letter of the equation:
hf = ɸ + KEmax
h = planks constant
f = frequency of incident wave
ɸ = work function of metal
KEmax = Make KE an emitted photoelectron can have (as KE varies but does have a maximum which is a result of the amount of energy above the work function)
What is the photoelectric effect?
When em radiation >ɸ is incident on the surface of a metal
- One election absorbs One photon 1:1 ratio
- Emitted electron is a photoelectron (Photon and electron)
Why is graphic suitable for DE Broglie’s electron diffraction experiment?
The spacing between atoms is similar to De Broglie wavelength
What is meant by ‘wave-particle duality’?
Em radiation / matter can display both wave & particle properties
How does the photoelectric effect explain that waves behave like particles?
It shows that waves behave like particles as there is no way to explain the results unless waves split into distinct particles.
Explain:
- Independent
- Dependant
- Control
variables
Independent - You change
Dependent - You then measure effect
Control - You keep the same to ensure a fair test
How does electron diffraction explain that particles behave like waves?
Diffraction pattern gives evidence for wave nature of electrons (or particles)
