5.2 - resistance & resistivity Flashcards
What is resistivity?
A measure of how difficult it is for current to flow through a material.
What is the equation for resitivity?
ρ = RA / L
ρ = resistivity (Ωm)
R = resistance (Ω)
A = area (m²)
L = length (m)
What is the relationship between resistivity and resistance?
As resistivity increases, resistance increases.
If the temperature increases what happens to resistance?
It also increases.
What is a thermistor?
A resistor with a resistance that depends on its temperature.
Is a thermistor ohmic or non-ohmic?
Non-ohmic.
If resistance decreases in a thermistor, what happens to the temperature?
The temperature increases.
What does a thermistor graph look like (resistance against temp)?
A curved inwards line with negative gradient.
What are 2 applications of thermistors?
- Circuits in ovens
- Circuits in fire alarms
What is the type of thermistor in this specification?
NTC thermistors (negative temperature coefficient).
If the temperature in a thermistor decreases, what happens to the rest of the circuit?
Potential difference across the thermistor increases.
What is the critical temperature?
The (very low) temperature at which a material is considered a superconductor.
What is a superconductor?
A material with no resistance below a critical temperature.
What is a common superconductor and what is its critical temp?
Mercury
C.T = 4.2K
What are 2 useful things superconductors produce?
- The production of strong magnetic fields
- The reduction of energy loss
