3.12 - DEFINITIONS Flashcards
Anode?
a positively charged electrode
Cathode rays?
beams od electrons emitted from a cathode through thermionic emission
Cathode?
a negatively charged electrode
Discharge tube?
A sealed glass tube held at low pressure, with an anode at one end and a cathode at the other. When the elctrodes are connected to a supply, the gas in the tube will glow and coonduct electricity.
Electron gun?
A pair of electrodes that produce a thin and fast moving beam of electrons
Negative glow?
A glow found near the cathode in a discharge tube; caused by the recmbination of positive ions with the electrons produced by ionisation, resulting in photons being emitted
Paddle wheel?
a whee found in a dischage tube that demonstrates the presence of cathode rays
Specific chage?
the ratio of mass to charge
Stopping potential?
a value of potetial difference a which photoelectric emission is stopped; this is because the electrons no longer have sufficient kinetic energy to cross the potential difference
Drag force?
A force acting against the oil drop’s motion in Millikan’s Oil Drop experiment - all objects going though a fluid will experience this
Quantisation of electric charge?
Charge can only be found in packets of energy with a charge that is a multiple of the electron charge
Black-Body?
A body that emits all wavelengths of radiation, dependant on its temperature
Ether?
A substance that was believed to fill all space and be responsible for light propagation
Fizeau’s determination of the speed of light?
An early method of determining the speed of light; timing the length of time it toom for a beam of light to travel to and back from a mirror by passing it through a rotating cog wheel
Hertz’s discovery of radio waves?
radio waves are produced when sparks jump across a gap of air; can be detected with a dipole detector or a wire loop with a gap in it.
Huygens’ Wave Theory?
AA theory stating that all wavefronts consist of a series of points from which secondary wavelets are emitted
Maxwell’s electromagnetic theory?
EM waves consist of oscillating, perpendicular electric and magnetic fields
Newton’s corpuscular theory?
A theory that light existed as discrete packets, referred to as corpuscles, that travel in straight lines and have momentum
Ultraviolet catastrophe?
The discrepancy between practical measurements and classical theoretical predictions of the energy intensities at different wavelengths, emitted from a black body
Work function?
The minimum energy required to remove an electron from a metal’s surface
