Electrons and energy levels

Question 1

What is a photon?

Answer 1

The name given to a discrete packet of EM energy

Question 2

What is the intensity of EM radiation?

Answer 2

The energy transferred per unit time per unit area.
It obeys an inverse square law.

Question 3

What is an electron volt?

Answer 3

The energy needed to move an electron through a potential difference of one volt.
W= VQ

Question 4

What happens when an electron absorbs a photon?

Answer 4

If the photon has the right amount of energy, the electron moves to a higher energy level

Question 5

What is the ground State?

Answer 5

The lowest energy state an electron can be in

Question 6

What happens when an electron moves to a higher energy level.

Answer 6

Excitation has occured. This happens when either

• a photon with the exact amount of energy to move up two energy levels, is absorbed
• Absorbing exactly the right amount of energy to move between two levels, after colliding with a free eletron.

Question 7

What happens when ionisation occurs in an atom?

Answer 7

An electron has gained enough energy to move from its ground state, to infinity

Question 8

What is a diffraction grating?

Answer 8

a piece of transparent material, with very closely spaced lines.

Question 9

what is a continuous spectrum?

Answer 9

a spectrum, where all frequencies of radiation, or colours of light are visible.

Question 10

What is a line spectrum?

Answer 10

a spectrum of discrete coloured lines.

Question 11

What is an emission spectrum?

Answer 11

a spectrum produced when electrons in atoms fall from higher energy levels to lower levels, and emit a photon

Question 12

What is an absorption spectrum?

Answer 12

A spectra that appears when light shines through a gas. Electrons in gases atoms absorb photons corresponding to the possible energy transitions.

Question 13

What happens when an electron moves to a lower energy level?

Answer 13

A photon is emitted, where the energy is equal to the energy lost.
E2-E1 = hf

Question 14

What is flourescence?

Answer 14

When a substance absorbs short wavelength EM radiation and emits it as a longer wavelength of radiation.

Question 15

What is a fluorescent tube?

Answer 15

a type of light bulb that gives out light, when its inner coating fluoresces

Question 16

What is thermionic emission?

Answer 16

When free electrons are released from a heated filament

Question 17

How does a fluorescent tube work?

Answer 17

• it’s a glass tube filled with mercury gas, and coated with phosphors.
• When it’s turned on, the cathode is heated, causing thermionic emission.
• this releases free electrons with a range of energies.
• a PD of 500v is applied across the ends of the tube.
• This accelerates electrons from the cathode to the anode.
• If they collide with the mercury atoms inelastically, some energy may be transferred to the mercury atoms.
• When the mercury atoms become ionised, a mixture of ions and free electrons is created, called a plasma
• When the excited electrons return to their ground state, they release UV photons, which strikes the phosphor and the energy is re-emitted as visible light.