Electricity Flashcards
(13 cards)
what is current?
current is the rate of flow of charge
what is potential difference?
potential difference is the energy (work done) per unit charge
what is ohms law?
provided that physical conditions (like temperature) remain constant, the current is proportional to potential difference
how do current and potential difference act in a parallel circuit?
current splits depending on the resistance in each branch
voltage is constant everywhere
definition of power
rate of work done
what happens to cells in series?
emf’s add together
current increases
battery runs out quicker
what happens to two cells of equal emf in parallel
the total potential difference in the circuit will be equal to that of one cell
no change in current
battery lasts longer
what happens to resistance of a resistor as temp increases and why?
resistance increases
atoms in the resistor are vibrating more
so more frequent collisions with electrons slowing their rate of flow
what happens to resistance of a thermistor as temperature increases and why?
resistance decreases as temp increases
more available electrons to carry the charge
what is a superconductor?
a material where the resistance and resistivity become zero at the ‘critical temperature’ which is around -260 degrees (-10K)
so no energy is lost to heat
three uses of a superconductor
power cables
MRI
particle accelerators
really strong magnets (maglev trains)
fast electronic circuits
definition of EMF
energy per unit charge transferred to the charge carries in the cell
what are ‘lost volts’?
potential difference lost in a cell due to the cells internal resistance
