Modern Physics - Definitions - Level 3 Flashcards
Ionisation
Ionisation is the ability of nuclear radiation to take an electron off an atom, making it an ion.
Rest mass
The mass of a particle is a variable which increases with speed. The rest mass is the mass of the particle when it is stationary.
Radioactivity
Radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability. Radiation is emitted by nuclear isotopes which are unstable.
Alpha emission
The release of an alpha particle (2+ helium ion or helium nucleus) from an unstable nucleus
Electron volt
An electron volt is the amount of energy required to move one electron (charge in joules) between two points with the voltage difference of 1 volt.
(1 eV = 1.6 x 10^-19 J)
Cutoff voltage (Vo)
The cutoff voltage is the voltage applied against the voltage in the plate to stop electrons with maximum velocity from ejecting from the metal. The photocurrent becomes zero with the cut-off voltage.
(Maximum opposing voltage that pushes the electrons back to the cathode with maximum kinetic energy and velocity).
Beta emission
The release of high-energy electrons as ionizing radiation (causes a neutron to convert into a proton) from an unstable nucleus
Nuclear fusion reaction
Nuclear fusion is a nuclear reaction in which two or more atomic nuclei collide at a very high speed, and join to form a new type of atomic nucleus.
- During this process, matter is not conserved because some of the matter of the fusing nuclei is converted to photons (energy).
Half-life
The half-life of a radioactive substance is the time after which exactly one-half of the originally active nuclei remain, being a measure of how quickly radioactive decay (disintegration) takes place.
Binding (Ionisation) energy
Binding energy is the energy required to completely remove an electron from an atom.
Nuclear binding energy
Nuclear binding energy is the energy required to split the nucleus of an atom into its constituent parts (nucleons - protons and neutrons).
Mass defect
The mass defect is the difference between the mass of a nucleus and the sum of the masses of its constituent particles (nucleons).
Binding energy per nucleon
The binding energy per nucleon is the total work done pulling the nucleons from a nucleus divided by the number of nucleons. The more work required to do this, the greater the binding energy per nucleon, and the more stable the nucleus of an atom.
Absorber
An absorber is a material that prevents radioactive emissions from passing through it.
Background radiation
Background radiation is the nuclear radiation that arises naturally from cosmic rays and radioactive isotopes in the soil and air.
Cathode rays
Negatively charged particles (electrons) are emitted from a negative terminal in an evacuated glass tube.
Continuous spectra
The continuous spectrum is the separation of the electromagnetic spectrum into its discrete frequencies with no gaps (missing frequencies).
Controlled nuclear fission
Involves the slow and useful release of energy in a nuclear reactor.
Critical mass
Mass of fissionable material needed to sustain a chain reaction.
Electromagnetic spectrum
A family of waves (eg. light), that do not require a medium, are transverse, and at travel at 3 x 10^8 ms^-1 in a vacuum.
Energy absorption
The amount of energy taken in by an electron when excited.
Isotopes
Atoms of an element with the same chemical properties (same number of protons), but with different masses (number of neutrons).
Nuclear force
The nuclear force is the force of attraction between subatomic particles which bind the nucleus together.
Nuclear reactor
A steel vessel in which a controlled chain reaction of fissionable materials releases energy.
Quanta
The fixed amounts of energy absorbed or emitted by matter.
Spectra
The separation of the electromagnetic spectrum into its discrete frequencies (eg. ROYGBIV for visible light).
Threshold frequency (fo)
The threshold frequency is the minimum frequency of photons (incident radiation) that would cause electrons to be emitted from a metal surface.
(Just free the electrons from their atoms and hold them on the surface of the metal. Any frequency above the threshold will cause electrons to be emitted out from the metal).
Work function of a metal
The work function is the minimum energy required to just eject electrons from the surface of a metal (during the photoelectric effect). The energy of the work function is converted to heat which increases the temperature of the metal.
Photoelectric Effect
The photoelectric effect is the emitting of electrons from a metal when it is struck by a light beam (radiation), and the frequency of the incident radiation is larger than the threshold frequency (fo) of the metal. Meaning, that the energy of the radiation is greater than the work function of the metal, and there is sufficient energy in each photon for electrons to escape the attraction of their atoms.
Photon
A photon is a packet of electromagnetic radiation; that is a monochromatic (single frequency or wavelength) quantum of electromagnetic energy.
Nuclear fission reaction (chain reaction)
Nuclear fission is either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei).
- The fission process often produces free neutrons and photons in the form of gamma rays, and releases a very large amount of energy.
Wave-particle duality
Wave-particle duality is the concept that every particle may be described as either a particle or a wave. Different models of light explain the behaviour of light in different situations.
- When light passes through a double slit an interference pattern is produced, showing wave behaviour.
- Whereas, when light interacts with matter it behaves like a particle.
Excitation energy
Excitation energy is the energy required to
excite an atom from ground state (or lower
state) to a higher state.
