Particles and Waves Key Terms Flashcards
atom
The basic units of matter, made up of positively charged protons, negatively
charged electrons and neutral neutrons.
It is overall neutral.
radioactive decay
When unstable nuclei emit nuclear radiation in the form of an alpha particle,
beta particle or gamma ray in an attempt to become more stable.
isotope
Atoms of the same element with different numbers of neutrons in the nucleus.
OR
Atoms with the same atomic number but different mass number.
mass number (A)
Used alongside atomic number to identify a particular isotope.
Gives the total number of protons and neutrons in the nucleus.
atomic number (Z)
Used alongside mass number to identify a particular isotope.
Gives the number of protons in the nucleus.
alpha radiation
An alpha particle consists of 2 protons and 2 neutrons. It is the same as a
helium nucleus.
It has a relatively large mass and short range in air (3-5 cm).
It is positively charged and is absorbed by a single sheet of paper.
beta radiation
A beta particle is a fast moving electron.
It has a relatively small mass and longer range in air (15 cm).
It is negatively charged and is absorbed by 2-3 mm of aluminium.
gamma radiation
A gamma ray is a high energy electromagnetic wave.
It has no mass and a very long range in air (hundreds of metres).
It has no charge and is absorbed by 2-3 cm of lead.
nuclear equation
Used with isotope symbols to describe radioactive decays.
In all nuclear equations, both mass number and atomic number are conserved.
parent nucleus
The original nucleus before a reaction takes place.
daughter nucleus
The product produced in a nuclear reaction.
alpha decay
When an alpha particle is emitted from the nucleus of an atom.
For an original parent nucleus undergoing alpha decay, its:
• mass number (A) will decrease by 4
• atomic number (Z) will decrease by 2
beta decay
When a neutron decays into a proton and electron (and anti-neutrino).
The electron is fired out of the nucleus as a beta particle, whilst the proton
remains within the nucleus.
For an original parent nucleus undergoing beta decay, its:
• mass number (A) will remain unchanged
• atomic number (Z) will increase by 1
gamma decay
When a high-energy electromagnetic wave is emitted from the nucleus of an
atom in an attempt for it to become more stable.
For an original parent nucleus undergoing gamma decay, its:
• mass number (A) will remain unchanged
• atomic number (Z) will remain unchanged
lost mass
Describes the mass difference which arises due to sum of the masses of the
particles produced by a reaction being slightly less than the sum of the masses
of the particles before the reaction.
Einstein’s Mass-Energy Equivalence Principle
According to this principle, lost mass can be turned into energy, but energy can
also be turned into mass.
nuclear fission
The process in which an unstable, heavy atomic nucleus splits into two or more lighter nuclei (called fission fragments), with energy being released.
spontaneous fission
A type of nuclear fission that occurs when the nucleus randomly decays.
induced fission
A type of nuclear fission that occurs when the nucleus is bombarded by a
neutron, causing it to split.
chain reaction
When a nucleus undergoes induced fission, the released neutrons can go on to
hit other nuclei, causing further fission reactions, and the cycle repeats.
The process may be controlled (nuclear power) or uncontrolled (nuclear
weapons).
nuclear fission reactor
In nuclear power stations, nuclear fission is used to produce heat energy within
nuclear fission reactors. This is used to turn water into steam, which drives
turbines to generate electricity.
moderator
Used in nuclear fission reactors to slow down the fast moving neutrons
released in fission reactions.
nuclear fusion
The process of small nuclei joining together to form a larger nucleus, with
energy being released.
nuclear fusion reactor
Where nuclear fusion is used to produce energy.
Special conditions of high temperatures and pressures are required to create
the plasma in which the fusion reactions can take place.
plasma
A state of matter in which nuclear fusion reactions can take place.
irradiance
The power per unit area of electromagnetic radiation incident on a surface.
point source
A small, compact source that emits radiation uniformly in all directions.
E.g. we can assume that a small bulb is a point source
inverse square law
Irradiance is directly proportional to the inverse of the distance squared for a
point source of light.
light
An electromagnetic wave that travels at 3x108 ms-1
.
It reflects, refracts and diffracts.
wave-particle duality
The idea that light can act both like a wave and like a particle without
contradiction.
photoelectric effect
Provides evidence for the particle nature of light.
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.
photoelectron
An electron emitted from the surface of a material due to a photon incident on
the material.
photoemission
The emission of photoelectrons from the surface of a material in the
photoelectric effect.
photon
A particle of light that can also be thought of as a short burst of wave energy.
electroscope
Consists of a metal plate, metal rod and gold leaf.
The deflection of the gold leaf can be used to investigate the photoelectric
effect.
threshold frequency
The minimum frequency of a photon required to cause the emission of
photoelectrons from a metal surface.
work function
The minimum energy of a photon required to cause the emission of
photoelectrons from a metal surface.
photoelectric current
The number of photoelectrons emitted each second from the surface of a
material.
interference
- provides evidence for the wave nature of light.
- observed when coherent waves overlap.
coherence
When two or more waves have the same frequency, wavelength and speed.
Waves produced from the same source are likely to be coherent.
Waves are said to be coherent if they have a constant phase difference.
phase
Describes how ‘in tune’ two waves are when overlapping.
Two waves are completely in phase when the crest of one matches up with the
crest of the other.
Two waves are completely out of phase when the crest of one matches up
with the trough of the other.
constructive interference
When two waves of equal amplitude meet in phase, they combine to form a
wave of twice the amplitude.
destructive interference
When two waves of equal amplitude meet out of phase, they combine to form
a wave of zero amplitude.
monochromatic light
light of a single frequency (or wavelength)
interference fringes
A series of bright and dark bands corresponding to regions of constructive and
destructive interference respectively.
path difference
The difference in distance travelled by waves from different coherent sources.
maximum/maxima
a point/points of constructive interference
minimum/minima
a point/points of destructive interference
order number (m)
an integer (whole number) value which describes the point on the interference pattern (screen) you are dealing with.
grating
Consists of many equally spaced slits placed very close together.
Light diffracts through each slit.
Lets much more light through compared to a double slit, so the fringes
produced are brighter and sharper.
