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20 terms

Electricity (OCR Physics A)

Key words and definitions for the Electricity part of Unit G482 of OCR Physics A (AS Level). Created by Rob Cowen, Head of Physics (
the charge transferred by a 1 ampere current in one second
1 joule per coulomb
the resistance when 1 volt of potential difference produces 1 ampere of current
kilowatt-hour (kW h)
the energy transferred by a 1 kW device in a time of 1 hour
electronvolt (eV)
the energy transferred by an electron travelling through a potential difference of 1 V
electric current
flow of charge per unit time
number density
the number of charged particles per unit volume
= potential difference / current
(resistance x cross-sectional area) / length
work done per unit time
potential difference
energy transferred per unit charge from electrical energy into other forms (e.g. light or heat)
electromotive force
energy transferred per unit charge into electrical energy from other forms (e.g. chemical)
internal resistance
some energy is lost as heat in the battery; it behaves as if it has an internal resistance
terminal p.d.
the potential difference measured across the terminals of an e.m.f. source
conventional current
moves from positive to negative terminals of battery
electron flow
moves from negative to positive terminals of battery
Kirchhoff's first law
sum of current into a junction equals the sum of current out; charge is conserved
Kirchhoff's second law
sum of e.m.f.s around a loop = sum of p.d.s around the same loop; energy is conserved
mean drift velocity
the average speed of charged particles along the length of a conductor
Ohm's law
for a metallic conductor at a constant temperature, the voltage is proportional to the current