C10 - Resistance and resistivity Flashcards
what 2 factors determine the size of the current
- potential difernace (Voltage) across the lamp greater v = greater current
- the resistance of the lamp
what is the equation for resistance
resistance = voltage/current
what is resistance measured in
ohms
what is the definition of the ohm
the ohm is the resistance of a component when the potential difference of 1 volt is produced per amp of current
how can you tell the resistance from a I-V graph that has a striangt line going through the origin
1/gradiant of graph
what is the definition of ohms law
ohms law states that for a metallic conductor at a constant temperature the current is directly proportional to the potential difference (voltage) across it.
what do we call something that obeys hooks law
an ohmic component
what are thermistors
these are resistors that are designed to have a resistance that changes rapidly after certain temperatures
what is a negative temperature coefficient
these are resistors that decree in resistance as the temperature increase
positive temperature coefficient
these resistors suddenly increase greatly in resistance after it goes above a certain temrpature
what 2 factors affect the resistance of a metal
- temperature
2. the presence of impurities
why does temperature affect the resistance of a metal
at a low temperature the free electrons can move easily pass the positive ions. however as the temperature increase these ions gain energy and start to vibrate, this cause the electrons to bump into them more which obstructs there flow (reduces mean flow velocity) so the resistance increases.
how is resistance proportional to its shape
resistance is proportional to length/c.s.area
what is resistivity
reistivity is a measure of its conductivity, and is a constant for a material as long as the temperature remains consistent
what is the equation for its resistivity
resistnace x c.s.area / length
