12. Electric current Flashcards
What is electrical current?
The rate of flow of charge
What is the convention for current?
Current flows from positive to negative
What is charge?
The charge flow in one second when the current is 1A
Why can’t an insulator conduct electricity?
Electrons are attached to an atom rather than free flowing, no charge carriers
Why can metallic conductors conduct electricity?
Some electrons are delocalised - charge carriers, they are attracted towards the positive terminal - flow of current
Why can semiconductors conduct electricity to an extent?
Number of charge carriers increase with an increase of temperature, resistance decreases
What is potential difference?
The work done per unit charge
What is Ohm’s law?
Potential difference and current is directly proportional given that any physical conditions remain constant
How does temperature change affect differently a positive and negative temperature coefficient?
Positive: Temperature increases, resistance increases
Negative: Temperature increases, resistance decreases (TURD)
What is the resistivity of a material?
The resistance of a conductor of a particular unit cross-sectional area and unit length - a constant value
What is a superconductor and what are the required conditions for a material to be superconducting?
A wire/device that’s made of material that has zero resistivity at and below its critical temperature, material is now superconducting
