Resistance Flashcards
What is the resistance of a component?
the measure of the difficulty of making current pass through the component
r = v / i
unit ohm which is equal to 1 volt per ampere
How is resistance measured?
ammeter is used to measure the current, must be in series (so the same amount of current passes through both the resistor and ammeter)
the voltmeter is used to measure the pd across the resistor, must be in parallel so they both have the same pd
What can a variable resistor do?
adjust the current and pd
What does the graph of a resistor look like?
straight line through the origin (directly proptional)
pd across the resistor is propotional to the current
What is resistivity?
ρ = RA/L
units ohm metere, Ωm
How is resistivity determined?
measure diameter at several points to find the mean
calculate its cross sectional area
measure the resistance at different lengths of the wire to plot a graph of R against L
the resistivity of the wire is given by the graph gradient x 4
What is a superconductor?
a wire or device made of a material that has zero resitivity at and below a critical temperature that depend on the material
What are the properties of a superconductor?
when a current passes through it, there is no pd across it because the resistance is 0, the current has no heating effect
What is the highest critical temperature acheived?
in 2014 it was 150K (-123 degrees celsius)
compund containing mercury, barium, calcium, copper and oxygen
What is a high-temperature superconductor?
any material with a criticial temperature above 77K
What are superconductors used for?
high-power electromagnets that generatre very strong magnetic fields in devices such as MRI scanners and particle accelerators
these strong magnetical fields are also used in the development of new applications such as lighweight electric motors and power cables that transfer electrical energy without dissipation
