Electricity – Leaving Certificate Physics Terms

Leaving CertificatePhysics

  • Coulomb – the unit of electric charge
  • Insulator – a substance in which electricity does not flow
  • Conductor – a substance in which electricity flows
  • All static charge lies on the – outside of a conductor
  • Static charge on a conductor accumulates – where the conductor is more pointed
  • Coulomb’s law – force equals charge 1 times charge 2 divided by 4 pi epsilon distance squared
  • Relative permittivity of a medium – permittivity divided by the permittivity of free space
  • Electric field – a region of space where a static charge experiences a force due to its charge
  • Electric field line – a line drawn in an electric field showing the direction of the force on a positive charge
  • Electric field strength – force / charge = charge divided by 4 pi epsilon distance squared
  • Unit of electric field strengthNewton / Coulomb or Volt / metre
  • Potential difference – work done in moving +1C of charge in an electric field
  • Unit of potential difference – Joule / Coulomb = Volt
  • Electric current – flow of electric charge
  • Potential at a point – potential difference between a point and the earth
  • All points on a conductor carrying static charge – are at the same potential
  • Capacitance – charge divided by voltage
  • Unit of capacitance – Farad
  • Farad – Coulomb divided by Volt
  • Capacitance of parallel plates – permittivity times area divided by distance
  • Energy stored in a charged capacitor – 0.5 times charge times voltage squared
  • The size of an electric current – the amount of charge passing a point in one second
  • Conventional current – flows plus to minus
  • Sum of currents flowing into a junction – equals the sum of currents flowing out of the junction
  • Potential difference – energy converted or work done when a charge of one coulomb is moved in an electric field
  • Electromotive force – sum of all voltages around a complete circuit
  • Voltages in series – V1 + V2 + V3
  • Voltages in parallel – V1 = V2 = V3
  • Primary cell – a cell which cannot be recharged
  • Secondary cell or accumulator – a cell which can be recharged
  • Simple cell – two different metal plates placed in an electrolyte
  • Resistance – voltage divided by current
  • Unit of resistance – ohm
  • Ohm’s law – voltage divided by current is constant at constant temperature
  • Resistors in series – R total = R1 + R2 + R2
  • Resistors in parallel – inverse of total resistance equals sum of inverses of resistances
  • Resistance of a metal – increases linearly with temperature
  • Resistance of a semiconductor – decreases non linearly with temperature
  • Thermistor – semiconductor resistance decreases rapidly as temperature increases
  • Resistivity – resistance times area divided by length
  • Unit of resistivity – ohm metre
  • Balanced wheatstone bridge – R1 / R2 = R3 / R4
  • Potential divider – gives any voltage from zero to the voltage supplied
  • Heat energy from electric current – current squared times resistance times time
  • Electric power – current squared times resistance
  • Chemical effect of electric current – electric current can cause chemical change
  • Chemical changes – chemical changes can give electric energy
  • Copper anode – copper metal dissolves to give copper 2+ ions and 2 electrons
  • Copper cathode – copper 2+ ions gain 2 electrons to form copper metal
  • Ionatom or molecule which has lost or gained one or more electrons
  • Charge carriers in an electrolyte – positive and negative ions
  • Charge carriers in metal – electrons
  • Charge carriers in semiconductors – electrons and holes
  • Applications of chemical effect – electrolysis electroplating extraction of ores purifying metals electrolytic capacitors
  • Live wire – voltage varies from + 325 volts to – 325 volts
  • Neutral wire – voltage about zero when device off
  • Earth wire – safety wire connecting metal parts of device down to ground in case of accident
  • Ring circuit – power fed along both sides of the ring to the sockets
  • Switch always connected in the – live wire
  • Fuse – a piece of wire which melts when a certain current passes through it
  • Fuse always connected in the – live wire
  • MCD miniature circuit breakers – contain a bimetallic strip and an electromagnet
  • MCD bimetallic strip trips – small current
  • MCD electromagnet trips – large current
  • RCD residual current device trips – difference between current in live and neutral exceeds a given value usually 30 millAmps
  • RCD residual current device trips – very quickly and so protects against electrocution
  • Bonding – all metal water pipes in a house must be connected to earth
  • Kilowatt hour – the amount of energy used by a 1000 Watt device in one hour
  • MCD miniature circuit breakers work – contacts pulled apart when a specific current is exceeded
  • Kilowatt hour in joules – 1000 Watts times 3600 seconds equals 3.6 Megajoules
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