Quantum Physics Flashcards
Photon
A photo is a massless packet of discreet quantity of electromagnetic energy.
Photon energy equation
E=hf E=hc/wavelength
Photon momentum
P=E/c
Define electronvolt
The energy gained by an electron travelling through a potential difference of 1 volt
What is the relation of electron volt to kinetic energy
ev=1/2mv^2
Convert from ev to j
Multiply by 1.6x10^-19
What is the photoelectric effect
Is the phenomenon in which electrons are emitted from the surface of a metal upon the absorption of electromagnetic radiation
The electrons removed are called photoelectrons
How does the photoelectric effect provide evidence that light is quantized
Each electron can only absorb a single photon
This means only frequencies of light above a threshold frequency will emit a photoelectron
Describe the photoelectric effect using the gold leaf electroscope
A plate of metal is attached to a gold leaf, which initially has a negative charge, causing it to be repelled by a central negatively charged rod. This causes a negative charge
Uv light is shone onto the metal plate, leading to the emission of photoelectron
Less negative charge so gold leaf falls
What would happen by placing the uv light closer to metal plate
Gold leaf will fall more quickly
As intensity incidents increase
This increases the number of photo electrons emitted per second
What would happen by using a higher frequency on gold leaf
Doesn’t change how quick gold leaf falls
Ke Inc with frequency but freq and ke are both independent of intensity
What would happen by using a filament lamp yo the gold leaf
No change in gold leaf position
Incident freq below threshold freq
Threshold frequency
The minimum frequency of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal
Threshold wavelength
Longest wavelength of incident electromagnetic radiation that would remove a photoelectron from the surface of a metal
Photoelectric equation
Threshold energy + ke of photoelectron
E=hf= threshold energy +1/2mv^2max
Threshold energy
The minimum energy required to release a photoelectron from the surface of a metal
What is wrong in wave theory
1) any freq of light can give rise to photoelectric emission if the exposure is long enough
2) the energy absorbes by each electron increases gradually with each wave
3) ke of emitted electrons should increase with radiation intensity
How do waves show wave particle duality
By diffraction
If there is a low accelerating voltage, what happens to the radius of diffraction rings
Increases
If there is a high accelerating voltage, what happens to the radius of diffraction rings
Decreases
De brogli wavelength
The wavelength associated with a moving particle
De brogli wavelength equation
Wavelength=h/p
Wavelength= h/mv
E=1/2mv^2
So E=p^2/2m p=squareroot(2mE)
Wavelength= h/squareroot(2mE)
What are the 2 types of spectra
Emission
Absorption
Emission spectra
Emission of a photon
(Dark with colored lines)
Absorption spectra
Absorb a photon
(Coloured dark line)
Calculating discrete energy levels
^E = hf = E2-E1
Wavelength=hc/(E2-E1)
What provides evidence to show electrons in atoms can only transition between discrete energy levels
The line spectrum in not continuous but rather contains only discrete values of wavelength
