Quanta definitions

Question 1

Quantum Theory

Answer 1

Used to explain a number of experimental observations that classical physics
could not.

Question 2

Black Body

Answer 2

A surface that absorbs all wavelengths of electromagnetic radiation but also
emits electromagnetic radiation at any wavelength.

Question 3

Black Body Radiation

Answer 3

The continuous spectrum of radiation emitted by a black body.
The curve has a characteristic shape.

Question 4

Ultraviolet Catastrophe

Answer 4

When two physicists developed an equation which fitted the observed black
body graph but only at long wavelengths. At shorter wavelengths (higher
frequencies), their graph tended to infinity.
Their equation had made the assumption that energy was added continuously
as the frequency of the radiation increased.

Question 5

Photoelectric Effect

Answer 5

Photoelectrons are ejected from the surface of a metal when photons of light

with sufficient energy are incident on the surface.
For photoemission to occur:
* the energy of the photons must be greater than the work function of the
metal
* the frequency of the photons must be greater than the threshold
frequency.

Question 6

Photoelectron

Answer 6

An electron emitted from the surface of a material due to a photon incident on
the material.

Question 7

Photoemission

Answer 7

The emission of photoelectrons from the surface of a material in the
photoelectric effect.

Question 8

Photon

Answer 8

A particle of light that can also be thought of as a short burst of wave energy.

Question 9

Threshold Frequency

Answer 9

The minimum frequency of a photon required to cause the emission of
photoelectrons from a metal surface.

Question 10

Work Function

Answer 10

The minimum energy of a photon required to cause the emission of
photoelectrons from a metal surface.

Question 11

Irradiance

Answer 11

The power per unit area of electromagnetic radiation incident on a surface.
It can be associated with the intensity or brightness of the incident light.

Question 12

Bohr Model of the
Atom

Answer 12

A model of the atom which describes the arrangement of electrons within it.
It proposes that electrons are in circular orbits around the nucleus which
correspond to energy levels.
The electrons can only occupy discrete energy levels; the ground state or an
excited state.

Question 13

Ground State

Answer 13

The lowest energy orbit.

It is the orbit closest to the nucleus of an atom.

Question 14

Excited State

Answer 14

An energy level above the ground state.

Electrons can move into an excited state when they gain energy.

Question 15

Quantised

Answer 15

When a quantity exists only in discrete chunks/packets. E.g. an integer multiple.

Question 16

Wave-Particle Duality

Answer 16

The idea that light can act both like a wave and like a particle without contradiction.

Question 17

Electron Diffraction

Answer 17

When electrons are incident on multiple tiny slits, interference fringes are
produced.

Question 18

Compton Scattering

Answer 18

An experiment involving the scattering of x-rays from electrons in a carbon
target. The scattered x-rays were observed to have a longer wavelength than
the incident x-rays.

Question 19

de Broglie Wavelength

Answer 19

The wavelength associated with an orbiting electron.

It explains the stability of orbits in the Bohr model of the atom.

Question 20

Uncertainty Principle

Answer 20

It is not possible to measure the position and the momentum of a particle with
absolute certainty. The more accurately one of these is known, the less
accurately the other is known.
In other words, it is not possible to know the position and the momentum of a
quantum particle simultaneously.
It is also not possible to know the lifetime of a quantum particle and the
associated energy change simultaneously.

Question 21

Quantum Tunnelling

Answer 21

Consider an electron facing an energy barrier where it requires a certain
amount of energy to get to the other side.
In classical physics, if the energy of the electron is below the energy barrier
then it will remain on the side that it is on.
In quantum physics, the electron can be treated as a wave function and there
is a finite probability that it can tunnel through the barrier and appear on the
other side.

Question 22

Cosmic Rays

Answer 22

Energetic subatomic particles which arrive in the Earth’s atmosphere from
outer space.
They are made up from 89% protons, 9% alpha particles, 1% carbon, oxygen
and nitrogen nuclei and the rest electrons and gamma rays.

Question 23

Cosmic Air Shower

Answer 23

The showers of secondary particles (electrons, photons, neutrinos and muons) that are produced when cosmic rays hit the top of the atmosphere.

Question 24

Solar Wind

Answer 24

Consists of a stream of charged particles which escape from the upper
atmosphere of the Sun. It flows outwards as a plasma at great speed and
consists mainly of electrons, protons and alpha particles.

Question 25

Aurorae

Answer 25

Cosmic particles trapped in the Earth’s magnetic field come down into the
atmosphere near the north and south poles. Nitrogen and oxygen molecules
become excited and when they return to their ground state they emit light.

Question 26

Simple Harmonic
Motion

Answer 26

When an object oscillates with a repeated motion under the influence of an
unbalanced force (restoring force) which always acts towards the equilibrium
position (rest position).
The magnitude of the unbalanced force is proportional to the object’s
displacement, but in the opposite direction.

Question 27

Damping

Answer 27

When an oscillating system loses energy to frictional forces such as air
resistance and eventually comes to rest.
The amplitude of the motion decreases to zero because energy is lost from the
system (i.e. it changes to other forms).