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Electricity Def

Physics definitions

Insulator any substance through which electric charge cannot flow
Conductor any substance through which electric charge can flow
Electric field an electric field is any reegion of space where a static electric charge experiences a force other than the force of gravity. It's always caused by other static charges in the vecinity
Line of Force a line drawn in an electric field showing the direction of the force on a positive charge placed in the field
Electric field strength at a point in an electric field is the force per unit charge at that point ie force per coulomb
Electric current is a flow of electric charge
Potential difference (between two points) in an electric field is the work done in bringing a charge of +1C from one point to the other
Potential differennce (in a circuit) between two points is the amount of energy converted from electrical to other forms between the two points when 1C charge passes any point of that circuit
Capicitance of a conductor is the ratio of the charge on the conductor to its potential C=Q/V
The Farad when placing a charge of 1C on a conductor raises its potential by 1 volt. 1farad=1C/V
Size of an electric current in a conductor is the amount of charge passing any point of that conductor per second
Electromagnetic force a voltage whe applied to a circuit
Resistance of a conductor is the ratio of the p.d across it to the current flowing through it R=V/I
Ohm a conductor has a resistance of one ohm if the current through it is 1 Ampere when th p.d across it is 1 Volt
Resistivity if a conductor of length l and cross-section area A has a resistance R the constant p is given by p=RA/l
Ion an atom or molecule that has lost or gained one or more electrons is called an ion
Kilowatt hour the amount of energy used by 1,000W appliance in one hour
Semi-conductor a substance whose resistivity is between between that of a good conductor and a good insulator. The resistivity of a semiconductor decreases as its temperature increases
Holes when an electron breaks free from a covalent bond, it leaves behind a gap in the atom from which it came- this gap is a positively charged hole
Intrinsic conduction conduction in a pure semi-conductor due to electrons moving from negative to positive and an equal number of holes moving in the opposite direction
Extrinsic conduction increased conduction in a semi-conductor due to the addition of impurities
The thermistor is a semi-conductor whose resistance decreases rapidly with increasing temperature
LDR conductivity is increased when light shines on it
Doping the adding of small controlled amounts of certain impurities to a pure semi-conductor to increase its conductivity
N-type semiconductor the impurity added produces more free electrons available for conduction ie phosphorus
P-type semiconductor the impurity added produces extra holes which are available for conduction ie boron
P-N junction is a piece of semiconductor with part of it doped p-type and the rest doped n-type
Depletion layer is the region at both sides of a p-n junction that contains no free majority charge carriers. It thus behaves as an insulator
Junction voltage the p.d that exists across a p-n junction caused by holes and electrons moving across the junction when it was formed is called the junction voltage
Magnetic field is any region of space where magnetic forces can be felt. The direction of the magnetic field at a point is the direction of the force on a north pole if it were placed at that point
Magnetic field line a line drawn in a magnetic field so that the tangent to it at any point shows the direction of the magnetic field at that point
the magnetic flux density (B) at a point in a magnetic field, is a vector whose magnitude is equal to the force that would be experienced by a conductor of length 1m
carrying a current or 1A at right angles to the field at the point and whose direction is the direction of the force on a north pole placed at that point
The tesla the magnetic flux density at a point is 1 tesla if a conductor of length 1m carrying a current of 1A experiences a force of 1N when placed perpendicular to the field
The Ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible cross section and placed 1m apart in a vacuum, would produce a force on each conductor of 2x10^-7 newtons per metre of length
The Coulomb is the amount of charge that passes any point in a circuit when a current of 1A flows for 1second
Electromagnetic induction whenever the magnetic field passing through a coil changes an emf appears in the coil
The Weber if the magnetic flux density over an area of 1m^2 is 1 tesla then the flux through the area is 1 weber
Electric generator is a device that converts mechanical energy to electrical energy
Mutual Induction if a changing magnetic field in one coil causes an induced emf to appear in a nearby coil there is said to be mutual induction between the two coils
Self Induction whenever the current passing through a coil changes the magnetic field surrounding
Transformer is a device used to change the value of an alternating voltage
Thermionic emission is the giving off of electrons from that surface of a hot metal
Cathode rays streams of high speed electrons moving from the cathode
The electronvolt is the emission of electrons from the surface of a metal by electromagnetic radiation of a suitable frequency
Threshole frequency metal the frequency below which photoemmision will not occur for a given. Light of frequency above the threshold frequency will cause photoemission
Work function of a metal is the minimum energy needed to remove the loosest electron from the surface of that metal
Photon is a packet of electromagnetic energy. The energy E of a photon is given by E=hf, where f is its frequency and h is Planck's constant
X-rays are high frequency electromagnetic radiation produced when high speed electrons in a cathode ray tube strike a metal target that has a high melting point
Emission spectrum the resulting pattern when light from a luminous source undergoes dispersion
Energy level is a fixed energy value an electron in an atom can have
Atomic number of an element is the number of protons in the nucleus of an atom of that element
Mass number the total number of protons and neutrons in the nucleus of an atom
Isotopes atoms of an element that have the same number of protons but different numbers of neutrons
Radioactivity is the disintegration or decay of the nuclei of certain atoms with the emission of one or more types of radiation
Alpha α radiation is fast moving hekium nuclei ejected from the nuclei of radioactive atoms
Beta β radiation is high-speed electrons ejected from the nuclei of radiation atoms
Gamma γ radiation is high frequency electromagnetic radiation (with frequencies above those of normal X-rays) emitted from the nucleus of a radioactive atom
Activity of a radioactive substance is the number of nuclei of that substance decaying per second
Half-life of a radioactive isotope/element is the time taken for: half of the undecayed atoms to undergo decay, :its activity to decrease by half
The Mole of any substance is the amount of that substance that contains as many particles as there are atoms in exactly 12g of the c-12 isotope (avagadro's number)
Nuclear Fussion is the joining of two small nuclei to form a larger nucleus
Nuclear Fission is the splitting up of a large nucleus into two smaller nuclei of roughly the same size
Pair production is the creating of two particles from energy. In the process a particle and its anti-particle are produced. Momentum and electric charge are conserved
An elementary particle is a particle that has no other particles inside it or has no subparts to it
Leptons is a particle that does not feel the strong force
Hadron a particle that feels the strong force
Quarks are elementary particles out of which baryons and mesons are made. They have a charge of +-1/3 or +-2/3 e
A meson is made up of any one quark and any one anti-quark
A baryon is made up of any three quarks
An anti-baryon is made of any three anti-quarks
Created by: Nya411
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