Topic 5: Electricity Flashcards
Electric charge
The cause of electric fields and currents. Either positive or negative. Q=It
Coulomb
The charge which passes a point when 1 A flows for 1s. 1C = 6.25 x 1018 electronic charges. e = 1.60 x 10–19C
Electric potential energy
The energy gained when work is done moving a charge in an electric field.
Electric potential difference
The work done per unit charge moving a positive test charge between two points in a circuit. V=W/Q measured in volts.
Volt
Unit of PD. One joule of electric potential energy is transferred to other forms when one coulomb flows between two points.
Electronvolt
The energy required to move one electron through a PD of one volt. W (eV) = q (electron charges) x V (volts). The formula below calculates the kinetic energy gained by an electron accelerated through a PD.
Electric current
The rate of flow of charge. Unit is the ampere. Conventional current flows from + to –.
Resistance
The ratio of PD across a conductor to current through the conductor. R=V/I. Unit is the ohm (Ω): 1Ω = 1V/A
Resistivity
An electrical property of a material
Ohm’s Law
The current through a metallic conductor is directly proportional to the voltage across its ends if the temperature and other conditions are constant.
Non-ohmic conductor
A conductor which does not obey Ohm’s Law ie V is not proportional to I.
Power
The rate of converting energy. Unit is watt (W) = 1J/S
EMF
The total electrical energy given by the battery to each coulomb of charge OR the terminal PD of the source when no current flows.
Internal resistance
The resistance of the battery. Some of the energy provided by the source is converted to heat here and is not available in the external circuit components.
Terminal PD
The PD measured across the terminals of the source which is less than the EMF due to the internal resistance of the source.
