Turning Points in Physics (Option 4) Flashcards
Anode
A positively charged electrode.
Bertozzi’s Experiment
An experiment that investigated the velocity of electrons emitted with different kinetic energies. It showed that the speed of light was never exceeded and that as the kinetic energy continually increases, the velocity of the electrons continually approaches the speed of light.
Black-Body
A body that emits all wavelengths of radiation, dependent on its temperature.
Cathode Rays
Beams of electrons emitted from a cathode through thermionic emission.
Cathode
A negatively charged electrode.
Condenser Lens
The lens in a TEM that is responsible for deflecting the electrons into a wide beam, that is then incident of the sample.
Constant Current STM
A form of scanning tunnelling microscope in which the current of the probe remains constant, and the probe’s height changes with changes in the sample’s surface. The current that tunnels across varies depending on the height, allowing an image to be formed.
Dipole Detector
A pair of aligned metal rods placed at the centre of a concave reflector.
Discharge Tube
A sealed glass tube held at low pressure, with an anode ar one end and a cathode at the other. When the electrodes are connected to a supply, the gas in the tube will glow and conduct electricity.
Drag Force
A force acting against the oil drop’s motion in Millikan’s Oil Drop experiment. All objects travelling through a fluid will experience drag.
Electron Gun
A pair of electrodes that produce a thin and fast moving beam of electrons. Electrons are emitted from the cathode by thermionic emission and are then accelerated through a gap by the anode.
Ether
A substance that was believed to fill all space and be responsible for light propagation.
Ether Drift
A theory that the Earth’s ether carried light along with it. This implied that light should travel faster when travelling in the direction of the ether, however, this was later proved to be false.
Fizeau’s Determination of the Speed of Light
An early method of determining the speed of light. It involved timing the length of time it took for a beam of light to travel to and back from a mirror, by passing through a rotating cog wheel.
Hertz’s Discovery of Radiowaves
Hertz discovered that radiowaves are produced when sparks jump across a gap of air. They can be detected with a dipole detector or a wire loop with a gap in.
Huygens’ Wave Theory
A theory stating that all wavefronts consist of a series of points from which secondary wavelets are emitted.
Inertial Frame of Reference
A frame of reference which is not accelerating (frames which travel at a constant velocity relative to each other).
Invariance of Speed of Light
The speed of light is identical for all observers, whatever the speed of the source is and whatever the observer’s state of motion is.
Length Contraction
For an observer moving parallel to a rod, the rod will appear shorter than for an observer at rest relative to the moving rod.
Maxwell’s Electromagnetic Theory
Maxwell predicted that a type of wave, known as an electromagnetic wave, consisted of oscillating, perpendicular electric and magnetic fields. He then went onto produce an equation for their speed, which combined with experiments, proved his theory.
Michelson-Morley Interferometer
An experimental set-up involving a monochromatic light source, a semi-silvered glass block, a plane glass block, two mirrors, and a viewing telescope. It proved that the speed of light is invariant.
Negative Glow
A glow found near the cathode in a cathode ray tube. It is caused by the recombination of positive ions with the electrons produced by ionisation. This results in photons being emitted.
Newton’s Corpuscular Theory
A theory that light existed in discrete packets, referred to as corpuscles, that travel in straight lines and have momentum.
Objective Lens
The second lens in a TEM microscope. It is responsible for the magnifying and focusing of the image of the sample.
