electricity Flashcards
kirchhoffs first law
the current passing through 2 or more components in series is the same throughout each component, and the sum of the currents entering a junction is equal to the sum of the currents leaving a junction.
kirchhoffs second law
for 2 or more components in series, the total p.d across the components is equal to the sum of the p.d across each component, and the sum of the emfs around a complete loop is equal to the sum of the p.ds in the loop
current
rate of flow of charge, the charge that passes a point per unit time
emf
electromotive force. energy gained per unit charge in the power supply
diode
appliance that allows current to flow in one direction through it.
internal resistance
resistance inside a source of electrical energy; the loss of p.d per unit current in the source when the current passes through it
light dependant resistor (LDR)
a resistor which had a resistance that changes with light intensity. as light intensity increases, resistance decreases
negative temperature coefficient thermistor
a component whose resistance decreases when its temperature is increased
ohms law
the p.d across a metallic conductor is proportional the the current, provided the physical conditions do not change (eg the temperature)
potential difference
work done per unit charge between 2 points when charge moves from one point tot he other
potential divider
2 or more resistors connected in series connected to a source of p.d
resistance
pd/current. the ratio of the potential difference across the component to the current flowing through it
resistivity
material property. is the resistance when current flows through 1m of wire with a cross-sectional area of 1m^2
semiconductor
a material in which the number of charge carriers increases when temperature is raised. more electrons are realsed by ionising the material.
explain resistivity in a semiconductor
electrons are held in the bonds between particles. not many electrons are mobile and able to carry a charge, so the material has a high resistivity at this point. resistance causes the material to heat up. when the material gets hot enough, some of the bonds are broken and more electrons are mobile and able to carry a charge
explain the shape of a resistance - temperature graph of a metal conductor
liner graph with y intercept > 0.for pure metals, the temperature of the material, the greater the kinetic energy of the molecules, so the molecules vibrate more and cause resistance to the flow of electrons.
superconductor
a material that has zero electrical resistance below a critical temperature.
what is the gradient of and IV-characteristic graph
rate of change of current with respect to potential difference
give 3 applications of superconductors
MAGLEV trains. MRI scanners. Power lines.
how do you work out the total resistance of a series circuit
add the individual resistances together
how do you work out the total resistance of a parallel circuit
1/Rtotal = 1/R1 + 1/R2 + …
what is terminal potential difference
is the potential difference across the terminal of the cell. in questions, can be used as if it is the emf of a cell with no internal resisitance
define power
rate of energy transfer
describe an ammeter
measures current. has negligible resistance so it doesn’t affect the circuit it is placed in. placed in series with the component being investigated.
