Modern Physics Flashcards
Thermionic emission
The release of electrons from the surface of a hot metal
Cathode rays
Streams of high speed electrons moving from the cathode to the anode in an evacuated tube
The electron volt
The energy gained or lost by an electron when it moves through a potential difference of 1V
Photoelectric effect
The release of electrons from the surface of a metal when light of suitable frequency falls on it
The threshold frequency
The minimum frequency needed for photoemission to occur for a given metal
Photon
A packet of electromagnetic energy
Work function
The minimum energy required by a photon to remove an electron from the surface of a metal
X-rays
High frequency electromagnetic radiation which are produced when accelerated electrons strike a metal target
An emission spectrum
Produced when light from a luminous source undergoes dispersion
Atomic number (Z)
The number of protons in an elements nucleus
The mass number (A)
The total number of protons and neutrons in the nucleus of an atom
Isotopes
Atoms that have the same atomic number but different mass numbers due to a different number of neutrons in the nucleus
Radioactivity
The decay of a nucleus with the spontaneous emission of radiation
Alpha radiation
Helium nuclei ejected from the nucleus of radioactive atoms
Beta radiation
High speed electrons ejected from the nuclei of radioactive atoms
Gamma radiation
High frequency electromagnetic radiation emitted from the nuclei of radioactive atoms
Ionisation
Occurs when atoms become charged by losing or gaining electrons
Electron
The sub atomic particle that orbits the nucleus
Activity
Number of nuclei decaying per second
Becquerel
Unit of activity equal to 1 disintegration per second
Law of radioactive decay
The activity of a sample is directly proportional to the amount present
Half life
The time taken for half the atoms present to decay
Nuclear fission
The splitting up of a large nucleus into two smaller nuclei of roughly the same mass with the release of energy
Nuclear fusion
The joining up of two smaller nuclei to form a larger nucleus with the release of energy
