Physics

• Scalar


  A quantity that has size only
• Vector


  A quantity that has size and direction
• Mass


  The amount of matter in an object
• Weight


  The force acting on the object due to the pull of gravity
• Hooke's law


  The extension of a spring is directly proportional to the force applied provided the limit of proportionality is not exceeded
• Principle of moments


  When a body is in equilibrium the sum of the clockwise moments will equal the sum of the anticlockwise moments about the pivot
• Centre of gravity


  The point on an object where all of the weight may be considered to act
• Principle of conservation of energy


  Energy can be changed from one form to another but the total amount of energy does not change
• Renewable energy resource


  Energy that will be replaced in less than a human lifetime and so will never run out
• Non-renewable energy resource


  Energy that cannot be replaced in a human lifetime so will run out
• Efficiency


  The fraction of the total input energy (into a device) that is transferred usefully
• Power


  The amount of energy transferred in one second
• Kinetic energy


  The energy a body has due to its motion
• Gravitational potential energy


  The energy a body has due to its height above the earth's surface
• Mass number


  The number of protons and neutrons in an atom
• Atomic number


  The number of protons in an atom
• Isotope


  Atoms of the same element with the same atomic number but different mass numbers
• Radioactive


  When an unstable nucleus decays to become more stable giving out some form of radiation e.g. alpha, beta, gamma
• Alpha particle


  A particle consisting of 2 neutrons and 2 protons emitted from an unstable nucleus in radioactive decay
• Beta particle


  A fast moving electron emitted from an unstable nucleus in radioactive decay
• Gamma ray


  High energy electromagnetic wave emitted from an unstable nucleus in radioactive decay
• Background activity


  The activity that can be measured when all other known sources of radiation are removed from the area
• Half-life


  The time taken for the count rate of a radioactive source to halve
• Fission


  When a heavy nucleus e.g. uranium, absorbs a neutron and splits into two lighter nuclei emitting 2/3 neutrons and energy
• Fusion


  When two light nuclei e.g. hydrogen are joined together producing a heavier more stable nucleus (e.g. helium) giving out energy
• Transverse wave


  A wave in which the particles vibrate perpendicular to the direction of wave travel
• Longitudinal wave


  A wave in which the particles vibrate parallel to the direction of wave travel
• Ultrasound


  A sound that has a frequency above 20,000 Hz
• Wavelength


  The distance between two neighbouring crests or troughs of a transverse wave or the distance between two compressions of a longitudinal wave
• Frequency


  The number of waves produced by a source each second OR the number of waves that pass a certain point each second
• Wave amplitude


  The maximum displacement of a particle in wave from its undisturbed position
• Law of reflection


  The angle of incidence equals the angle of reflection
• Dispersion


  The splitting up of white light into different colours
• Spectrum


  The range of colours produced when white light undergoes dispersion
• Focal length


  The distance between the principal focus and the centre of a lens
• Ohm's Law


  At a constant temperature the current through a conductor is directly proportional to the voltage across it
• Alternating current


  Current which changes direction periodically
• Direct current


  Current which always flows in the same direction
• Kilowatt hour (kWh)


  The amount of electrical energy used by a device of power 1000W in one hour
• Double insulation


  When an appliance has all of its live internal components completely encased in an insulator