3. Photons and Lasers

Question 1

Photon

Answer 1

The smallest possible amount of light energy

Question 2

Absorption

Answer 2

When electrons on lower energy levels receive photons of an energy that matches the change in the energy levels

Question 3

Emission

Answer 3

When the electron releases a photon back into space

Question 4

Ionisation

Answer 4

When an electron is moved up or down an energy level depending on how much energy it has

Question 5

Ionisation energy

Answer 5

The energy needed to knock an electron out of its energy level
The energy needed to move an electron from its ground state

Question 6

Stimulated emission

Answer 6

The emission of a photon from an excited atom which is triggered by an incident photon of energy equal to the gap between the excited state and lower energy level.

Question 7

Population inversion

Answer 7

When more electrons (more populated) are on a higher energy level than the one below it

Question 8

Pumping

Answer 8

When an electron receives a photon of the same energy difference and then moves up to a higher energy level

Question 9

Photoelectric effect

Answer 9

The release of electrons from the surface of a metal when electromagnetic radiation is incident on its surface. This then reduced the overall charge of the object.

Question 10

Work function (WF)

Answer 10

The minimum amount of energy needed by an electron to allow it to move off the surface of a metal

Question 11

Max kinetic energy of electrons

Answer 11

Ekmax = hf - WF

Question 12

Threshold frequency

Answer 12

The minimum frequency for which photoelectrons are emitted

The Ekmax would be 0

Question 13

Electron volt (eV)

Answer 13

The amount of kinetic energy an electron will receive after being accelerated through 1V

Question 14

Stopping potential

Answer 14

The amount of volts needed to show the ammeter reading as 0

Question 15

V stop equation

Answer 15

Ekmax = e x Vstop

Question 16

Change in energy equation

Answer 16

E2 - E1

Question 17

Photon energy equation

Answer 17

E = hf (- WF)

Question 18

Alternate photon energy equation

Answer 18

E = hc / wavelength (-WF)

Question 19

What are the quantities gathered from a Graph of KE against Frequency

Answer 19

Gradient = Plancks constant

Y-intercept = The work function x -1

Question 20

Milikans experiment

Answer 20

The experiment to find the Vstop of an electron by using a circuit.
Measured the frequency of light and also the KE of the photons that are emitted off the metal surface.

Question 21

Wave particle duality

Answer 21

The ability of waves to behave as particles and as waves

Question 22

Conductor

Answer 22

A material through which electrons can flow easily

Question 23

Insulator

Answer 23

A material in which electrons cannot flow easily

Question 24

Electroscope

Answer 24

A device used to detect the existence of electrical charge

Question 25

Absorption spectra

Answer 25

A rainbow spectrum with black lines, this shows the certain frequencies of light radiated.

Question 26

Emission spectra

Answer 26

A black background with coloured lines, it represents the electrons moving through different energy levels. They loose energy as they produce a photon which then creates emission lines.

Question 27

Monochromatic

Answer 27

Photons or waves of a single wavelength

Question 28

Coherence between incident and emitted photons

Answer 28

The relationship between the incident photon and the emitted photon is coherent as they are the dame frequency and in phase

Question 29

Gas laser pros and cons

Answer 29

Large
Expensive
Inefficient
However, used when the laser needs to produce a specific wavelength

Question 30

Semiconductor / laser diodes pros and cons

Answer 30

Small
Cheap
Very Efficient
Most common and used for eye surgery / image scanning
cant produce high power

Question 31

Metastable

Answer 31

When an energy level in a laser is almost stable to hold electrons without spontaneous emission

Question 32

Ionisation energy

Answer 32

The energy needed for an electron to escape the atom, the energy needed is just above the highest energy level
(In an exam question if it asks for the ionisation energy then write the highest energy level)

Question 33

Light Amplification

Answer 33

The stimulation causes double the amount of photons to be emitted. (exponentially increases)

Question 34

Different types of lasers

Answer 34

2 level energy system
3 level
4 level

Question 35

Excitation

Answer 35

When an electron gains more energy and moves to a higher energy level

Question 36

Spontaneous emission

Answer 36

When an electron drops to a lower metastable level and emits a photon

Question 37

What is the photo electric effect

Answer 37

When photons are incident upon a metal surface with the same wavelength as the electrons. this causes the electrons to eject from the surface

Question 38

What is the de broglie wavelength

Answer 38

wave length = h / momentum
we use this equation as the size of the gap needed to diffract them cannot be achieved easily

Question 39

What is the radiation pressure

Answer 39

The change in momentum of electromagnetic radiation, this then causes pressure to be exerted upon a surface

Question 40

What is electron diffraction?

Answer 40

When electrons are accelerated towards graphite crystals they create a diffraction pattern.
This proves they have wave like properties

Question 41

Structure of a typical laser

Answer 41

There is an amplifying medium between two mirrors, 99% is reflected and the other 1% is transmitted as the laser light