【正文】 ha decay.Alternating current: An electric current that varies in magnitude and direction periodically with time. Alternating voltage: An electric voltage that varies in magnitude and direction periodically with time.Ammeter: An instrument that is connected to an electric circuit to measure current, Ampere: The SI unit of electric current. One ampere is equal to one coulomb per second.Archimedes39。 principle: The upthrust on an object immersed in a liquid is equal to the weight of the liquid displaced by that object.Atomic mass constant: The unified atomic mass constant, u, is equivalent to onetwelfth the mass or the carbon12 atom.Atomic mass number: The total number of nucleons (protons and neutrons) in a nucleus. It is also known as the nucleon number A.Background radiation: Low intensity radiation from radioisotopes found in the ground and atmosphere, as well as, cosmic rays that arrive at the surface of the earth.Becquerel: The SI unit of the activity of a radioisotope. One becqueret is equal to one disintegration per second.Beta decay: The spontaneous decay of an unstable atomic nucleus acpanied by the emission of a beta particle,Beta particle (radiation): A high speed electron that is emitted from a radioactive nucleus.Binding energy (nuclear): Binding energy is the equivalent energy liberated due to mass loss (mass defect) when separate nucleons form a nucleus.Binding energy per nucleon: The binding energy of the nucleus divided by the nucleon number or the mass number, A.Breaking stress: The maximum tensile stress at which an elongated wire will snap.Brittle material: A material that does not go through the plastic deformation when a tensile stress is applied.Capacitance: The ratio of the charge on either plate to the potential difference between them. Capacitor: A device that is capable of storing charges.Chain reaction, nuclear: A self sustaining reaction in which neutrons split a heavy nuclei to produce more neutrons that will cause further reactions to occur.Charge carrier: A particle that carries either a positive charge or a negative charge.Conductor, electrical: A material that has low resistivity and conducts electric current well because of the high concentration of 39。free electrons39。 in them.Conservation of charge: Electric charge cannot be created or destroyed,Control rod: A rod that is usually made of cadmium or boron that can absorb neutrons in a thermal fission reactor, thereby controlling the rate of a fission reaction.Conventional current: The flow of positively charged particles.Concave lens: A lens that diverges a parallel beam of light such that the divergent beam appears to e from a point called the principal focus.Convex lens: A lens that converges a parallel beam of light to a point called the principal focus. Coulomb: The SI unit of electric charge.Coulomb39。s law: The magnitude of the electrostatic force between two electrically charged bodies is proportional to the product of the charges and inversely proportional to the square of the distance between them.Count rate: The readings on a detector that indicate the average rate of emission of radiation from a radioactive source.Current voltage characteristics: The graph of current I against potential difference V of a circuit ponent.Daughter nucleus: The product of a radioactive decay or a nuclear reaction.De Broglie39。s equation: An equation that relates the momentum p of a moving particle to its wavelength.Decay constant: The probability of radioactive decay per unit time,Diode: A electrical device that permits electric current to flow through it in one direction onlyDuctile material: A material that could be drawn into a thin wire without breaking, cracking or showing signs of losing strength.Elastic deformation: The slight elongation or pression of a piece of material when a force is applied to it. In the absence of the force, the material returns to its original state immediately.Elastic limit: The point on the forceextension graph in which elastic deformation gives way to plastic deformation.Electrical energy: The energy stored in an electric charge in an electric field. Electrical power: The rate of work done in an electrical system.Electric charge: A property of some particles that interact with other particles in accordance with Coulomb39。s law.Electric current: Rate of flow of electric charges. Electric field: A region in space where an electric charge experiences an electric force.Electric line of force: The path along which a positive test charge will move in an electric field. These imaginary lines of force are used to represent the electric field around electric charges.Electric field strength: The electrostatic force per unit positive charge that acts at that point in the same direction as the force.Electric potential energy: The work done on the charge by an external force in bringing it from infinity to that point in the electric field.Electric potential: The work done in bringing unit positive point charge from infinity to that point in the electric field.Electric potential difference: The work done by an external force in moving a unit positive charge from a point at lower potential to a point at higher potential.Electromagnet: A solenoid that behaves like a magnet when a direct current flows through it.Electromagnetic induction: The production of an . whenever there is a change of magnetic flux linkage or when there is relative motion between a conductor and the magnetic field passing through it.Electromagnetic spectrum: A wide range of electromagnetic waves arranged in ascending order of wavelengths.Electromagnetic waves: Transverse waves consisting of electric and magnetic fields that oscillates perpendicularly to each other.Electromotive force: The chemical, mechanical or other forms of energy that is converted into electrical energy when unit charge passes through the source.Electron: A