Chapter 12 - Electric current #2 Flashcards
What is 1kWh in Joules?
6
1kWh = 3.6x10 J
Why do semiconductors have an increase of charge carriers with increasing temperature?
As with conductors, when a semiconductor is heated, particles within the lattice gain energy so the ions vibrate faster.
In semiconductors, heating the lattice will provide electrons bound to atoms with the required energy to be freed.
T↑, I↑, R↓
What is a superconductor?
A material which loses all of its resistance at or below a certain critical temperature.
There is no pd across a superconductor at or below its critical temperature as no energy is lost.
What is an LDR?
A resistor made of semiconducting materials that are sensitive to light.
Light intensity↑, I↑, R↓
What is resisitivity?
The constant of proportion in the relationship,
R ∝ L ÷ A
where L = length of wire
where A = cross-sectional area (πr2)
The degree to which the type of material resists the flow of charge carriers.
It is affected by temperature. To have a constant resistivity, the current should remain constant to prevent a temperature increase.
Give two uses of superconductors.
The production of strong magnetic fields and the reduction of energy loss in transmission of electric power.
A superconductor loses its superconductivity if…
…its temperature is raised at or above its critical temperature.
What is another term used for critical temperature of a superconductor?
Transition temperature
What is superconductivity?
A property of certain materials which have zero resistivity at and below a critical temperature which depends on the material.
What is the equation for resistivity?
What is the unit?
RA
ρ = ——–
L
Unit: Ωm
What is a semiconductor?
A substance in which the number of charge carriers increases when the temperature increases. Therefore, its resistance decreases as temperature increases (opposite of a metallic conductor).
Does a thermistor have a negative temperature coefficient?
Explain why.
A thermistor made from a semiconductor has a negative temperature coefficient as the number of charge carriers increases when the temperature is increased.
T↑, I↑, R↓
What is meant by the term negative temperature coefficient?
Resistance decreases with increase of temperature.
What is meant by the term positive temperature coefficient?
Give an example of something that has a positive temperature coefficient.
Resistance increases with increase of temperature.
A metallic conductor.
Give two applications of thermistors.
Temperature sensors and resistance–temperature graphs.
