Modern physics Flashcards
(25 cards)
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
photoelectric effect
The release of electrons from the surface of a metal when EM radiation of a suitable frequency falls on it
Photon
A discrete packet of electromagnetic energy. Its energy depends on its frequency.
E=hf
X-rays
High frequency electromagnetic radiation which are produced when high speed electrons strike a metal target of high melting point
An emission spectrum
Produced when light from a luminous source undergoes dispersion
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
Three forms of radiation
Alpha
Beta
Gamma
Ionisation
the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons
Activity (A)
The number of nuclei decaying per second
Law of radioactive decay
The activity of a sample is directly proportional to the amount present
Nuclear fission
The splitting of a large nucleus into two smaller nuclei of roughly the same mass with the release of energy
Nuclear fusion
The joining of two smaller nuclei to form a large nucleus with the release of energy
Properties of an electron
Negatively charged
orbits the nucleus
very small compared to proton/neutron
Properties of cathode rays
Travel in straight lines
Cause certain substances to fluorescence
produce x-rays
deflected by electric & magnetic fields
Photocell
A device that conducts electric current when light of a suitable frequency shines on it
Geiger-Muller tube
A device used to detect radiation
Moderator in a nuclear reactor
slows the neutrons to allow for fission to sustain a chain reaction
Control rod in a nuclear reactor
absorbs neutrons to control the rate of fission
Example of a moderator
Graphite/Heavy-water
Chain reaction
a self-sustaining reaction where the release of one or more neutrons causes further fission
Where does nuclear fusion most commonly occur?
The sun
Why are nuclear fusion reactors not yet viable?
Too much energy needed
