EM Radiation and Quanta Goodnotes Recap

Question 1

Surface Electron Emitted?

Answer 1

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

Question 2

Photoelectric Effect?

Answer 2

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

Question 3

Photo electrons?

Answer 3

The name for the electrons emitted in the photoelectric effect

Question 4

Threshold Frequency?

Answer 4

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

Question 5

No emitted electrons?

Answer 5

No photo electrons are emitted if the radiation frequency is below the threshold frequency

Question 6

High frequency radiation?

Answer 6

The maximum kinetic energy of the emitted electrons increases with a higher radiation frequency

Question 7

Intensity?

Answer 7

The amount of energy per second hitting an area of metal

Question 8

Intensity of radiation?

Answer 8

The maximum kinetic energy of the photo electrons is unaffected by changes in intensity of the radiation

Question 9

Intensity and number of photo electrons?

Answer 9

There is a directly proportional relationship between the number of emitted electrons per second and the intensity of the radiation

Question 10

Wave theory intensity?

Answer 10

According to wave theory the electromagnetic frequency of the energy carried by the wave should be directly proportional with the intensity of the beam

Question 11

Wave theory EM properties?

Answer 11

Wave theory suggests the energy carried by electromagnetic radiation would spread out evenly over the wave front

Question 12

Wave theory electrons?

Answer 12

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

Question 13

Wave theory EM wavelengths?

Answer 13

Wave theory would suggest low frequency EM waves would gain enough energy to cause the photoelectric effect

Question 14

Wave theory on photoelectric effect?

Answer 14

Intensity, energy, released electrons, frequency and free electrons all disprove wave theory and show how wave theory cannot explain threshold frequency

Question 15

Max Planck?

Answer 15

First scientist to suggest EM waves can only be released in discrete packets called quanta

Question 16

What is “E”?

Answer 16

The notation of the energy of each packet and is measured in joules in a series of equations regarding E = HF

Question 17

Einstein’s Photons?

Answer 17

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.

Question 18

Photoelectric Effect Experiment?

Answer 18

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.

Question 19

Photoelectric Effect Interaction?

Answer 19

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

Question 20

Work function?

Answer 20

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

Question 21

Work Function conditions?

Answer 21

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

Question 22

Work function equation?

Answer 22

F 0 = ϕ / h
Threshold Frequency = Work Function / Planck’s Constant

Question 23

Minimum energy?

Answer 23

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

Question 24

Energy Losses?

Answer 24

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

Question 25

Energy Photoelectric Effect Equation?

Answer 25

hf = ϕ + Ek (max) Planck's Constant x Frequency = Work Function + Maximum Kinetic Energy

Question 26

Kinetic Energy Photoelectric Equation?

Answer 26

Ek (max) = 1/2 m v (max)^2 Maximum Kinetic Energy = 1/2 x electron mass x maximum velocity of photo electron

Question 27

Rules of the photoelectric effect?

Answer 27

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

Question 28

Stopping Potential?

Answer 28

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

Question 29

Reason for stopping potential?

Answer 29

Photo electrons emitted by the photoelectric effect can lose their energy by doing work done against an applied potential difference

Question 30

Stopping Potential Equation?

Answer 30

e x Vs = Ek (max) charge of electron x stopping potential = maximum kinetic energy

Question 31

Electron energy?

Answer 31

Not normally measured in joules due to the amount of energy being so small

Question 32

Electron Volt?

Answer 32

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

Question 33

Electron Volt relationship?

Answer 33

The energy gained by an electron in electron volts (eV) is equal to the accelerating voltage (V)

Question 34

Joules to Electron Volt conversion?

Answer 34

1 eV = 1.6 x10-19 J

Question 35

Excited Electrons?

Answer 35

Electrons are only excited when their energy is higher than the ground state

Question 36

Energy Levels?

Answer 36

Electrons can only exist in well-defined energy levels and each level is given a number

Question 37

Ground State?

Answer 37

N = 1 represents the lowest energy of an electron can be at and is referred to as ground state

Question 38

Energy Level Movement Downwards?

Answer 38

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

Question 39

Photon Transition Energy?

Answer 39

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

Question 40

Energy Level Movement Upwards?

Answer 40

Electrons can move up energy levels only if they have a photon with the exact energy between the two energy levels

Question 41

Excitation?

Answer 41

The movement of an electron to a higher energy level

Question 42

Electron Transition Equation?

Answer 42

ΔE = E1 - E2 Change in energy in joules = energy in initial energy level - energy in new energy level

Question 43

Ionisation Energy?

Answer 43

The amount of energy to remove an electron from ground state

Question 44

Electron transitioning levels?

Answer 44

The energy of each energy level shows the amount of energy needed to remove an electron from that level

Question 45

Electron Removal from atom?

Answer 45

When an electron is removed from an atom the atom is ionised due to it having more positive charge than negative charge

Question 46

Fluorescent tubes?

Answer 46

They contain mercury vapour and use excitation and photon emission to produce visible light

Question 47

Fluorescent tube function?

Answer 47

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.

Question 48

Line Spectrum creation?

Answer 48

A line spectrum occurs when light from a fluorescent tube is split into its components from a prism or diffraction grating

Question 49

Diffraction grating and prisms?

Answer 49

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.

Question 50

Light Emission Spectrum?

Answer 50

A series of bright lines against a black background with each line corresponding to a particular wavelength of light emitted by a source

Question 51

Line spectra emission levels?

Answer 51

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.

Question 52

Prism property?

Answer 52

They can merge all colours of white light into one beam to make a colour spectrum with no gaps

Question 53

Continuous spectrum examples?

Answer 53

White light and hot objects (hot objects also emit an infrared spectrum)

Question 54

Property of continuous spectrum?

Answer 54

Electrons are free in a continuous spectrum

Question 55

Line absorption spectra creation?

Answer 55

A line absorption spectra is produced when white light with a continuous spectrum of energy passes through a cool gas

Question 56

Absorption and emission spectra?

Answer 56

The black lines on an absorption spectra will line up with the bright lines on the emission spectrum

Question 57

Line absorption spectra function?

Answer 57

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

Question 58

Diffraction?

Answer 58

When a beam of light passes through a narrow gap similar to the wavelength and spreads out

Question 59

Diffraction explanation?

Answer 59

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

Question 60

Wave particle duality?

Answer 60

The photoelectric effect and diffraction show how light is able to behave like a wave and particle

Question 61

Photoelectric effect relationship with electrons?

Answer 61

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

Question 62

Louis De Broglie?

Answer 62

Louis De Broglie said if light showed particle properties otherwise photons. Then particle like electrons should be able to show wave-like properties

Question 63

De Broglie Equation?

Answer 63

λ = h / mv De Broglie Wavelength = Planck's Constant / mass x velocity

Question 64

Peer Review?

Answer 64

The evaluation of a scientific report where experts go through the same area and examine if its clear and logical

Question 65

Electron Diffraction?

Answer 65

This was one of the experiments that was done to try and give evidence to validate the theory suggested by Louis De Broglie

Question 66

Electron Diffraction method?

Answer 66

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.

Question 67

Wave theory diffraction pattern trends?

Answer 67

The spread of lines in the diffraction pattern increase if the wavelength of the wave is greater

Question 68

Accelerating voltage trends?

Answer 68

In electron diffraction experiments if there is a smaller accelerating voltage the electrons go slower and the rings produced are more widely spread

Question 69

Electron Speed trend in diffraction grating experiment?

Answer 69

A higher electron speed results in the diffraction pattern with rings closer together

Question 70

De Broglie Equation evidence?

Answer 70

The de broglie equation shows when velocity is high the wavelength is shorter which means the spread of the diffraction pattern decreases

Question 71

Accelerated Electron Property?

Answer 71

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

Question 72

De Broglie Wavelength and Diffraction?

Answer 72

Diffraction can only happen if the interacting particle is the same size as the de broglie wavelength

Question 73

Mass and diffraction patterns?

Answer 73

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

Question 74

Electron Microscopes?

Answer 74

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