EM Radiation and Quanta Goodnotes Recap Flashcards
Surface Electron Emitted?
If radiation, typically in the UV range, is of a high enough frequency than it will result in an electron being emitted from the surface of a metal if shone directly on it
Photoelectric Effect?
Metals contain free electrons able to move up the metal. They absorb the energy from the radiation and consequently vibrate. If the electron absorbs enough energy the bonds holding the metal break and it is released from the metals surface
Photo electrons?
The name for the electrons emitted in the photoelectric effect
Threshold Frequency?
The frequency needed to emit the photo electrons and is the lowest frequency of light that when shone on a metal will cause electrons to be released because of the photoelectric effect
No emitted electrons?
No photo electrons are emitted if the radiation frequency is below the threshold frequency
High frequency radiation?
The maximum kinetic energy of the emitted electrons increases with a higher radiation frequency
Intensity?
The amount of energy per second hitting an area of metal
Intensity of radiation?
The maximum kinetic energy of the photo electrons is unaffected by changes in intensity of the radiation
Intensity and number of photo electrons?
There is a directly proportional relationship between the number of emitted electrons per second and the intensity of the radiation
Wave theory intensity?
According to wave theory the electromagnetic frequency of the energy carried by the wave should be directly proportional with the intensity of the beam
Wave theory EM properties?
Wave theory suggests the energy carried by electromagnetic radiation would spread out evenly over the wave front
Wave theory electrons?
If EM was shone on a metal surface each free electron on the surface of the metal would gain a small amount of energy from each incoming wavefront and all electrons would gain enough energy to leave the metal
Wave theory EM wavelengths?
Wave theory would suggest low frequency EM waves would gain enough energy to cause the photoelectric effect
Wave theory on photoelectric effect?
Intensity, energy, released electrons, frequency and free electrons all disprove wave theory and show how wave theory cannot explain threshold frequency
Max Planck?
First scientist to suggest EM waves can only be released in discrete packets called quanta
What is “E”?
The notation of the energy of each packet and is measured in joules in a series of equations regarding E = HF
Einstein’s Photons?
Einstein suggested EM waves and the energy they carry can only exist in discrete packets called photons. These photons have a one-on-one particle like interaction in a metal surface and transfers all its energy to one specific electron.
Photoelectric Effect Experiment?
Also called the gold leaf experiment. A zinc plate is attached to an electroscope containing a metal plate with a strip of gold leaf attached. The zinc is negatively charged. The negative metal repels the gold leaf. UV is shone onto the plate causing electrons to be removed from the plate. Gold leaf falls down as it is not negatively charged so isn’t repelled and falls back down.
Photoelectric Effect Interaction?
When EM radiation hits a metal the metal surface is bombarded by photons and if one of them collides with a free electron it will gain all the photons energy
Work function?
Has the symbol ϕ and is dependant on the metal and is the requirement of having enough energy to break the bond of the electron on the metal surface
Work Function conditions?
If the energy gained from the photon is greater than the work function there will be a photo electron emitted. If the energy gained from the photon is less than the work function the electron will vibrate more causing the metal to heat up in addition to releasing a photon in the opposite direction
Work function equation?
F 0 = ϕ / h
Threshold Frequency = Work Function / Planck’s Constant
Minimum energy?
The minimum amount of energy that can be lost by an electron and is the value of the work function of the released photo electron
Energy Losses?
The kinetic energy used to carry the electron away from the metal surface as well as other losses result in a range of kinetic energies from the use of the energy transferred to the electron from the absorption of a photon
Energy Photoelectric Effect Equation?
hf = ϕ + Ek (max)
Planck’s Constant x Frequency = Work Function + Maximum Kinetic Energy
Kinetic Energy Photoelectric Equation?
Ek (max) = 1/2 m v (max)^2
Maximum Kinetic Energy = 1/2 x electron mass x maximum velocity of photo electron
Rules of the photoelectric effect?
The kinetic energy of the electrons is independent of the value of intensity of the beam. Electrons can only absorb one photon at a time. Increasing intensity means more photons of the same energy per second on an area are being emitted
Stopping Potential?
A way of measuring the maximum kinetic energy of photo electrons and has the symbol “Vs” and the units in volts. It is the potential difference needed to stop the fastest moving electrons with kinetic energy
Reason for stopping potential?
Photo electrons emitted by the photoelectric effect can lose their energy by doing work done against an applied potential difference
Stopping Potential Equation?
e x Vs = Ek (max)
charge of electron x stopping potential = maximum kinetic energy
Electron energy?
Not normally measured in joules due to the amount of energy being so small
Electron Volt?
Has the symbol eV and is defined as the kinetic energy carried by an electron after it has been accelerated from rest through a potential difference of 1 volt
Electron Volt relationship?
The energy gained by an electron in electron volts (eV) is equal to the accelerating voltage (V)
Joules to Electron Volt conversion?
1 eV = 1.6 x10-19 J
Excited Electrons?
Electrons are only excited when their energy is higher than the ground state
Energy Levels?
Electrons can only exist in well-defined energy levels and each level is given a number
Ground State?
N = 1 represents the lowest energy of an electron can be at and is referred to as ground state
Energy Level Movement Downwards?
Electrons can move down an energy level by emitting a photon. This can only be between definite levels which means each photons take a specific and unique value
Photon Transition Energy?
The energy carried by a photon emitted after a transition is equal to the difference in energy between the two levels the electron is transitioning between
Energy Level Movement Upwards?
Electrons can move up energy levels only if they have a photon with the exact energy between the two energy levels
Excitation?
The movement of an electron to a higher energy level
Electron Transition Equation?
ΔE = E1 - E2
Change in energy in joules = energy in initial energy level - energy in new energy level
Ionisation Energy?
The amount of energy to remove an electron from ground state
Electron transitioning levels?
The energy of each energy level shows the amount of energy needed to remove an electron from that level
Electron Removal from atom?
When an electron is removed from an atom the atom is ionised due to it having more positive charge than negative charge
Fluorescent tubes?
They contain mercury vapour and use excitation and photon emission to produce visible light
Fluorescent tube function?
High voltage is applied to mercury vapour. This accelerates fast moving free electrons that then ionise other mercury atoms. When the free electrons collide with the mercury atoms the electrons in the mercury atoms are raised to a higher energy level. Excited electrons return to ground state and release high energy photons in UV range. The phosphorus coating absorbs the photons and excites phosphorus electrons. When the phosphorus electrons lose energy they emit low energy photons in the form of visible light.
Line Spectrum creation?
A line spectrum occurs when light from a fluorescent tube is split into its components from a prism or diffraction grating
Diffraction grating and prisms?
Diffraction gratings and prisms work by diffraction light by different wavelengths at different angles. Diffraction gratings create more defined patterns with clearer lines than diffraction prisms.
Light Emission Spectrum?
A series of bright lines against a black background with each line corresponding to a particular wavelength of light emitted by a source
Line spectra emission levels?
Line spectra provide evidence that electrons exist in different energy levels. Atoms can only emit photons with energy equal to the difference of two energy levels. The corresponding wavelength of these photons are visible on the line spectrum which is used to calculate their energy.
Prism property?
They can merge all colours of white light into one beam to make a colour spectrum with no gaps
Continuous spectrum examples?
White light and hot objects (hot objects also emit an infrared spectrum)
Property of continuous spectrum?
Electrons are free in a continuous spectrum
Line absorption spectra creation?
A line absorption spectra is produced when white light with a continuous spectrum of energy passes through a cool gas
Absorption and emission spectra?
The black lines on an absorption spectra will line up with the bright lines on the emission spectrum
Line absorption spectra function?
At low temperatures most electrons in the gas will be in ground state. Electrons absorb photons of correct wavelength and excite to a higher energy level. Black lines are produced as the wavelength of the photons missing from the continuous spectrum which don’t come out of the gas
Diffraction?
When a beam of light passes through a narrow gap similar to the wavelength and spreads out
Diffraction explanation?
Diffraction can only be explained using waves and if light was acting as a particle the beam would be unaffected when passing through the gap but this is not the case
Wave particle duality?
The photoelectric effect and diffraction show how light is able to behave like a wave and particle
Photoelectric effect relationship with electrons?
Light can be viewed as a series of particle light photons. As a photon is a discrete bundle of energy it can interact with electrons in a one to one way. All the energy in the photoelectric effect is transferred to a single electron
Louis De Broglie?
Louis De Broglie said if light showed particle properties otherwise photons. Then particle like electrons should be able to show wave-like properties
De Broglie Equation?
λ = h / mv
De Broglie Wavelength = Planck’s Constant / mass x velocity
Peer Review?
The evaluation of a scientific report where experts go through the same area and examine if its clear and logical
Electron Diffraction?
This was one of the experiments that was done to try and give evidence to validate the theory suggested by Louis De Broglie
Electron Diffraction method?
In an electron diffraction tube electrons are accelerated at high velocities in a vacuum and passed through a graphite crystal. As the electrons pass through the spaces between the atoms they diffract like waves.
Wave theory diffraction pattern trends?
The spread of lines in the diffraction pattern increase if the wavelength of the wave is greater
Accelerating voltage trends?
In electron diffraction experiments if there is a smaller accelerating voltage the electrons go slower and the rings produced are more widely spread
Electron Speed trend in diffraction grating experiment?
A higher electron speed results in the diffraction pattern with rings closer together
De Broglie Equation evidence?
The de broglie equation shows when velocity is high the wavelength is shorter which means the spread of the diffraction pattern decreases
Accelerated Electron Property?
The electrons accelerated in an electron diffraction tube are the same size as the EM waves in the x-ray part of the EM spectrum
De Broglie Wavelength and Diffraction?
Diffraction can only happen if the interacting particle is the same size as the de broglie wavelength
Mass and diffraction patterns?
If the particles have a greater mass and travelling at the same speed as an electron it will result in a diffraction pattern with its rings closer together. The particle also has more momentum which consequently causes it to have a shorter de broglie wavelength
Electron Microscopes?
A shorter wavelength gives a smaller amount of diffraction. Small details in images require shorter wavelengths. As light blurs more details than an electron wave it means electron microscopes resolve in higher detail and can produce images of things like DNA
