AS Science Unit 2 Module 4

Combustion: A reaction in which a fuel reacts with oxygen to produce heat energy - we often describe a combustion reaction as simply 'burning'.

Fossil Fuel: A substance formed from the fossilised remains of dead plants and animals, which can take part in a combustion reaction to produce heat.

Hydrocarbon: A molecule consisting of carbon and hydrogen only.

Atomic Number: The number of protons in a nucleus - sometimes called the proton number.

Mass Number: The total number of protons and neutrons in a nucleus - sometimes called the nucleon number.

Radioactivity: The ability of some types of unstable atom to emit energy in the form of particles or high frequency electromagnetic waves.

Isotopes: Atoms which have the same number of protons but different numbers of neutrons. E.g. C-14 and C-12.

Radiation: The emission of energy as (electromagnetic) waves or (moving subatomic) particles.

Radioactive Decay: This eventually happens to all atoms containing an unstable nucleus - it 'decays' and emits radiation. The original (parent) nucleus is transformed into a new (daughter) nucleus.

Radiation Dose: A measure of the effect which radiation has on cells. It varies depending on the energy of the radiation, the length of exposure and the type of the cell exposed.

Contamination: The spreading of a radioactive source into a particular area or object. The object itself becomes radioactive as it now contains a source of radiation.

Irradiation: The exposure of an area or object to radiation. Although ionisation and other chemical processes may occur, the object does not become radioactive as it does not contain a source of radiation.

Half-Life: The time taken for the number of atoms of a sample of a radioactive isotope to fall to a half of its original value.

Nuclear Fusion: Two nuclei join together to produce a single heavier nucleus. Very high temperatures are required to cause this to happen, but large amount of energy are released when fusion occurs.

Nuclear Fission: The splitting of a nucleus into lighter fragments, caused by the absorption of a neutron. Energy, in the form of gamma rays, other neutrons and heat are also produced.

Electrical Current: A flow of charge - in the case of metals, the charge will becarried by electrons. The unit of current is the amp (A) where 1A means that 1C (Coulomb) of charge flows in one second. Current = charge/time.

Direct Current (d.c.): Current in which the flow of charge is in one direction.

Voltage: aka 'potential difference'. This is a measure of the amount of energy that can be transferred when a charge moves between two points. The unit of potential difference is the volt (V) where 1V means that 1J of energy is transferred by each coulomb of charge.

Resistance: The ability of a material to resist the flow of electrical charge. Measured in ohms. Energy is transferred when current flows through a resistance. Resistance = voltage/current.

Power: The rate at which energy is transferred - the unit of power is the watt (W). A power of 1W means that 1J of energy is transferred every second.

Energy Transmission: The delivery of electrical power from power station to sub-station.

Energy Distribution: The delivery of electrical pwoer form a sub-station to consumers.

Energy Density: The energy released from 1kg of fuel.

Electric Field: A region of space around a charged object in which any other charged object may experience a force.

Magnetic Field: A region of space around a magnetic pole in which any other magnetic pole may experience a force.

Electromagnetic Field: A field of force that consists of both electric and magnetic components, resulting from the motion of an electric charge and containing a definite amount of electromagnetic energy.

Field Line: A line which shows the direction of movement of a + charge in an electric field, or a north pole in a magnetic field.

Epidemiology: The science of epidemiological studies in which the causes of disease, or the way in which it spreads, are investigated.