Quantum Phenomena

Question 1

State what is meant by a photon

Answer 1

Electromagnetic radiation is emitted, tranferred and absorbed in discrete packets called photons, a photon is a quanta of energy

Question 2

Define the electron volt

Answer 2

1 eV is the energy required to accelerate an electron through a pd of 1 volt

Question 3

Describe the energy level model of an atom

Answer 3

nucleus of an atom traps its electrons in a potential well consisting of a series of quantised energy levels, hence electrons have discrete energies in atoms

Question 4

What is excitation?

Answer 4

An electron is given energy to move up to a higher energy level

Question 5

What is ionisation?

Answer 5

An electron is removed from the atom

Question 6

Describe a continuous spectrum

Answer 6

All values of wavelengths present (hot black body under high pressure)

Question 7

Describe an emission line spectrum

Answer 7

Discrete values of wavelengths present, hence bright liines on dark background (hot gas under low pressure)

Question 8

Describe an absorption line spectrum

Answer 8

A continuous specteum with missing wavelengths, hence a series of dark lines on a bright background (hot black body under high pressure -> cooler gas)

Question 9

What is the significance of the photoelectric effect?

Answer 9

It provides evidence of the particulate nature of electromagnetic radiation

Question 10

Describe the photoelectric effect

Answer 10

When electromagnetic radiation is incident on the surface of a metal, the energy of a single photon is absorbed by a single electron. The electron is the released from the metal surface - a photoelectron. Energy is conserved in this interaction

Question 11

Define the threshold frequency

Answer 11

Minimum frequency of a single incident photon required to release a single electron from the surface of the metal

Question 12

What is meant by the work function?

Answer 12

The minimum energy required to release a single electron from the surface of a metal

Question 13

What is meant by the stopping voltage?

Answer 13

The minimum pd required to just stop the electrons from being emitted from the cathode

Question 14

Explain the significance of electron diffraction

Answer 14

The diffraction of electrons by thin crystals give eveidence for the wave nature of particles like electrons

Question 15

Explain the pattern of electron diffraction

Answer 15

Electrons travelling through polycrystalline graphite will be diffracted by the atoms and the spacings between atoms. Hence a diffraction pattern is produced. Rings are observed because the atomic crystals are in all possible orientations

Question 16

What is meant by the de Broglie wavelength?

Answer 16

Broglie suggested a particles momentum could be used to calculate its wavelength. The de Broglie wavelength of a particle is dependent on the speed or momentum of that particle

Question 17

How might the amount of electron diffraction change?

Answer 17

If the pd across the cathode anode is increased, the the max velocity increases, and the wavelength decreases, hence the amount of diffraction decreases

Question 18

State some applications of electron diffraction by matter

Answer 18

diffraction of electrons by matter can be used to determine the arrangement of atoms and the size of nuclei