2.2 resistance Flashcards
what is pd
work done moving a unit of charge between 2 points of a circuit
V = W/Q
what is resistance
pd across the component divided by current
ohms law
current through a conductor is proportional to the pd across it provided temp is constant
gradient of a current pd graph
1/ R
why does current increasing on a filament am cause an increase in the resistance
as current flows through the lamp, electrical energy is converted to heat energy so the metal ions vibrate with increased amplitude. this causes more frequent collisions between ions and electrons increasing resistance
describe the experiment to determine the resistivity of a metal
- measure d of wire with micrometer to calculate A
- set up circuit
- vary wire length and record V and I for each length
- use R+V/I to work out R
- plot resistance-length graph
- gradient = resistivity / A
- resistivity = gradient x A
what is power
the rate of energy transfer
what is a super conductor
a material that, when cooled below its critical / transition temperature, has a resitsivity of zero
applications of superconductors
- power cables - would reduce energy loss
- MRIs - strong magnetic fields which would not require constant power source
what is superconductivity
when a material conducts with zero resistance. a material will begin to do this when is cooled to below a certain temp.
what is the transitions / critical temp
the temp below which a superconductor must be cooled in order to have zero resistance
