# Electricity – Leaving Certificate Physics Terms

• 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     (No Ratings Yet) Loading ...

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