﻿ Glossary

Anode is a metal plate connected to a high potential (positive pole of a voltage source).

Cathode is a metal plate connected to a low potential (negative pole of a voltage source).

Cathode rays are electrons emitted from the negatively charged plate in a discharge tube.

Collector is the anode of a photocell.

Discharge tube is a partially evacuated tube in which electrons travel whenever a suitable voltage is applied between the electrodes in the tube.

Einstein's photoelectric equation

Electromagnetic waves are caused by the acceleration of charged particles. These waves involve electric and magnetic fields vibrating transversely and sinusoidally at right angles to the direction that the wave is travelling. The waves do not require a medium for propogation and travel through a vacuum at 300 million meters per second.

Electron is a tiny particle, which has negative charge.

Emitter is the cathode of a photocell.

Frequency is the number of oscillations per second (Unit: the Hertz)

Hertz (Hz) is a unit of frequency; equal to one oscillation per second.

Intensity is the amount of energy passing through unit area normal to the direction of the wave.

Kinetic Energy (KE) is the energy a body has by virtue of its motion.

Electron Volt (eV) is the energy acquired by an electron when it is accelerated by a potential difference of one volt.

Monochromatic one colour (i.e. waves of a single wavelength i.e. of a single frequency)

Nanometer is ten to the power of minus nine of a meter (one millionth of a milli-meter).

Potential Energy (PE) is the energy a body has by virtue of its position.

Photocell is a vacuum tube containing a concave cathode called an emitter, and a wire anode called a collector, which functions on the principle of the photoelectric effect.

Photoelectric effect is the emission of electrons from the surface of a metal when light of sufficiently short wavelength is incident on the metal.

Photons may be thought of as bundles of energy. The amount of energy in a photon is proportional to the frequency of the radiation.

Planck's constant, h, is the ratio of the energy of a photon to the frequency of the wave in which it travels. It is a universal physical constant.

Quantum Mechanics is the branch of physics that interprets physical phenomena occuring on a very small scale (e.g. the motion of electrons).

Quantum (plural: Quanta) is a packet of energy (another name for a photon).

Stopping potential is the voltage needed to stop the most energetic electrons from reaching the collector.

Thermionic emission is the emission of electrons from the surface of a metal when the metal is heated.

Threshold Frequency is the minimum frequency that photons must have if they are to liberate electrons from a particular metal.

Voltage is a measure (in volts) of the potential difference between two parts of an electrical circuit.

Wave is a transmission of energy.

Wavelength is the distance between two successive crests.

Work Function is the minimum energy that an electron needs in order to escape from a particular metal (by the photoelectric effect).