U2.5 Quantum Physics

Question 1

What is the equation for energy of a quantum?

Answer 1

E = h x f Or E = h x c ÷ λ

h = planks constant (data sheet)
c = speed of light in a vacuum (data sheet)
f = frequency of the radiation in Hz
λ = wavelength of radiation in m

Question 2

What happens to the energy of a quantum if frequency increases?

Answer 2

The energy of the quantum increases.

Question 3

What is a single packet of electromagnetic radiation called?

Answer 3

It is called a quantum or usually a photon for light.

Question 4

What is the equation for energy?

Answer 4

E = Q x V

Question 5

What is the intensity of radiation falling on / being emitted from a surface defined as?

Answer 5

The energy per second per square metre.

Question 6

What is photo electric emission?

Answer 6

Electrons are ejected from the surface of a metal when electromagnetic radiation (usually visible or UV) of frequency greater than the threshold frequency falls on its surface.

Emitted electrons are called photoelectrons.

This process can be called the photoelectric effect.

Question 7

What is observed during the photoelectric effect.

Answer 7

• The number of photoelectrons emitted per second is proportional to the intensity of the incident radiation.

• Emission only occurs when the frequency of the radiation is greater than a minimum value, called the threshold frequency, ƒ₀.

• the emitted electrons have a range of kinetic energies, from zero up to a maximum value which depends on the frequency of the radiation, but not the intensity.

Question 8

What is the definition of a photon?

Answer 8

A packet of electromagnetic radiation magnetic energy.

Question 9

What is the definition of work function?

Answer 9

The minimum energy needed to liberate an electron from the metal surface.

Question 10

What is the equation for work function?

Answer 10

W = h x ƒ₀

W = work function
h = planks constant
ƒ₀ = threshold frequency

Question 11

What is ground state?

Answer 11

It is when all the electrons in an atom are on the lowest possible energy level.

All other levels are called exited states.

Question 12

What is ionisation energy?

Answer 12

The energy required to allow an electron to escape from the atom.

Question 13

What is population inversion?

Answer 13

When there is more electrons in an upper energy state than the ground state.