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#deck:Brainlag::GCSE Physics key terms
#tags:brainlag gcse-physics
Isotopes	Have the same number of protons but different numbers of neutrons
Radioactive decay	Some nuclei are unstable. To become more stable they give out radiation
Activity	The rate at which nuclei in a source decay, measured in becquerels: 1 Bq is one decay per second.
Count rate	The number of decays it detects each second or minute.
Background radiation	Radiation is always around us from rocks, the air and space
Ionising	Knocking electrons off atoms.
Battery	Two or more cells joined together.
Ammeter	Measures current. It goes in series, in the same loop as the component.
Voltmeter	Measures potential difference. It goes in parallel, across the component's two ends.
Current	The rate of flow of charge: how many coulombs pass a point each second.
Potential difference	The push that drives charge through it. It tells you how much energy each coulomb of charge transfers: 1 volt is 1 joule per coulomb.
Resistance	How much a component opposes the current.
Ohmic conductor	For a fixed resistor at constant temperature the current is directly proportional to the p.d.
Kinetic energy store	Anything moving
Gravitational potential energy store	Anything raised up
Elastic potential energy store	Anything stretched or squashed
System	Just the object or group of objects you choose to look at.
Specific heat capacity	The energy needed to raise the temperature of 1 kg of a substance by 1 °C.
Work done	Energy transferred by a force.
Dissipated	Usually into the thermal store of the surroundings, where it spreads out and is no longer useful.
Non-renewable	Coal, oil, natural gas (the fossil fuels) and nuclear fuel. They are being used up faster than they can be replaced, and will run out.
Renewable	Wind, solar, hydroelectricity, tides, waves, geothermal and bio-fuel. Nature replaces them as fast as we use them.
Reliable (energy resource)	It can produce electricity whenever it is needed.
Scalar	A quantity with a size only
Vector	It has a size and a direction
Displacement	How far you end up from the start, in a straight line, and in which direction.
Contact forces	Need the objects to touch: friction, air resistance (drag), tension, the normal contact force from a surface, and upthrust in a fluid.
Non-contact forces	Act across a gap: gravitational force (weight), magnetic force and electrostatic force.
Centre of mass	The weight of an object acts as if it all pulls at one point
Resultant force	The single force that would have the same effect.
Resolving	Splitting one force into two parts at right angles.
Normal	An imaginary line at 90° to a surface, drawn where the ray hits it.
Specular reflection	A smooth surface (a mirror, still water) reflects parallel rays in a single direction, so you see a clear image.
Diffuse reflection	A rough surface (paper, a matt wall) scatters parallel rays in many directions.
Filter	Transmits its own colour and absorbs the rest.
Permanent magnet	Makes its own magnetic field all the time.
Induced magnet	A piece of magnetic material that becomes a magnet only while it sits in a field.
Magnetic field	The region round a magnet where a magnetic material or another magnet feels a force.
Alternating current (a.c.)	Its potential difference keeps swapping direction, so the current flows one way, then the other, many times a second.
Earth wire	A safety wire joined to any metal case. It is at 0 V and only carries a current if something goes wrong.
Transverse wave	The vibrations are at right angles to the direction the energy travels.
Longitudinal wave	The vibrations are along the same direction the energy travels.
Amplitude	The biggest displacement from the rest position, measured from the middle line to a crest.
Wavelength	The distance from a point on one wave to the same point on the next, such as crest to crest.
Frequency	How many waves pass a point each second, in hertz (Hz).
Period	The time for one complete wave to pass, in seconds.
Random error	Scatters readings both ways by different amounts (reaction time, a flickering display).
Systematic error	Shifts every reading the same way by the same amount.
Zero error	A systematic error: the instrument reads something when it should read zero.
Satellite	Anything that orbits a larger body.
Nebula	A cloud of dust and gas pulled together by gravity.
Galaxy	A huge group of billions of stars held together by gravity.
Light-year	The distance light travels in one year.