Electricity Flashcards
Back EMF
EMF induced in the spinning coil of an electric motor or in any coil in which the current is changing (e.g. the primary coil of a transformer). A back EMF acts against the change of applied pd.
Charge carriers
Charged particles that move through a substance when a pd is applied across it
Circuit rule for current (Kirchhoffs 1st Law)
- The current passing through two or more components in series is the same through each component.
- At a junction, the total current in = the total current out
Circuit rules for PD (Kirchhoffs 2nd law)
- For two or more components in series, the total pd across all the components is equal to the sum of the pd’s across each component.
- The sum of the emf’s round a complete loop in a circuit = The sum of the pd’s round the loop.
critical temperature of a superconducting material
temperature at and below which its resistivity is zero.
electrical conductor
an object that can conduct electricity
electrically insulating materials
an electrical insulator is a material that cannot conduct electricity; a thermal insulator is a material that is a poor conductor of heat
electrolysis
process of electrical conduction in a solution or molten compound due to ions moving to the oppositely charged electrode
electrolyte
a solution or molten compound that conducts electricity
electromotive force (emf)
the amount of electrical energy per unit charge produced inside a source of electrical energy
free electrons
electrons in a conductor that move about freely inside the metal because they are not attached to a particular atom.
Internal resistance
Resistance inside a source of electrical energy; the loss of pd per unit current in the source when current passes through it
Light dependent resistor (LDR)
Resistor which is designed to have a resistance that changes with the light intensity
Negative Temperature coefficient
The resistance of a semiconductor decreases when its temperature is increased
Ohm’s Law
The pd across a metallic conductor is proportional to the current as long as the physical conditions do not change
Positive Temperature Coefficient
The resistance of a metal increases when its temperature is increased
Potential Difference
The work done or energy transfer per unit charge between two points when charge moves from one point to the other
Potential Divider
Two or more resistors in series connected to a source of pd
Resistance
pd/current
Resistivity
Resistance per unit length x area of cross section
semiconductor
substance in which the number of charge carriers increases when the temperature is raised
simple electric motor
electric motor with an armature consisting of a single coil of insulated wire
superconductor
material that has zero electrical resistance
thermistor
resistor which is designed to have a resistance that changes with temperature
