4.5 Quantum Physics

Question 1

What is a photon

Answer 1

Discrete energy quanta (packets)

Question 2

What is an electronvolt (eV)

Answer 2

A unit of energy used to measure photons

1eV is the energy transferred when an electron travels through a p.d of 1V

Question 3

What is an electron vault in joules

Answer 3

1eV = 1.6 x 10^-19 J

Question 4

What is the photoelectric effect

Answer 4

When electromagnetic radiation is shone on a metal, electrons are released form the surface

Question 5

What is the photoelectric equation

Answer 5

Maximum kinetic energy (J) = (Planck’s constant x frequency (Hz) ) - work function (J)

KEmax = hf - φ

Question 6

What is the work function (φ) and state its units

Answer 6

The minimum energy required to release an electron from its surface

Joules (J)

Question 7

What happens if frequency of radiation on an electron is equal to the threshold energy

Answer 7

The electron will be released but it will have to be no kinetic energy

Question 8

What happens if frequency of radiation on an electron is greater than the threshold energy

Answer 8

The electron will be released with kinetic energy

Question 9

What is wave-particle duality

Answer 9

All matter can exhibit both wave and particle properties

Wavelength of a particle is inversely proportional to its momentum

Question 10

What is the de Broglie equation

Answer 10

Wavelength (m) = Planck’s constant / momentum (kgms ^-1)

λ = h/p

Question 11

What is evidence for wave-particle duality

Answer 11

Electrons have particle properties
- can be accelerated and deflected by magnetic / electric fields

They also have properties associated with waves
- can diffract between atoms