Chapter 8 Flashcards
Define current
The rate of flow of charge per second
Delta Q
————
Delta T
What is a coulomb?
Electric charge flowing past a point in 1 second if current is 1 amps
Define charge
A property that can be positive or negative
Electrons ions and protons are charge carriers
What is the charge of an electron?
-1.6 x10^-19 coulombs
How many electrons make up 1 coulomb?
1/1.6x10^-19 = 6.25 x10^18 electrons
Why is charge described as quantised?
Because it can only have specific values
What is electric current?
The flow of charge or movement of charge carriers(protons, electrons or ions
What is current in metals?
Flow of electrons from the negative end to the positive end. Metal atoms are fixed while delocalised electrons can carry charge
The structure of metals is a regular lattice of positive ions with delocalised electrons. Vibrations of ions increases temp
What happens if charge flow is faster?
Current is greater which means more electrons move past a point per second
Where does conventional current flow?
Positive terminal to negative(opposite to direction of electron flow(charge flow))
What are electrolytes?
Liquids that carry an electric current through ions. They are molten ionic compounds or ionic solutions
Why is electrolysis a current?
Negative ions go to the anode and positive ions go the the cathode. The movement of ions is the flow of charge
Positive ions accept electrons and negative ions donate electrons which flow around the circuit
What a conservation of charge?
Electric charge cannot be created nor destroyed. Electric charge in the universe is constant
What is Kirchhoff’s first law?
Charge and current is conserved. At any point in a circuit, sum of current going in = sum of current going out
What is number density?
The number of free charge carriers per cubic metre of a material.
Higher number density means it’s a better conductor
What number density do conductors have and give some examples
They have a number density of 10^28 m^3 order of magnitude. Examples are lead, zinc, copper.
They are metallically bonded so there are a lot delocalised electrons
What number density do semiconductors have and why?
They have lower than conductors with order of magnitude of 10^17m^-3.
Usually group 4 elements: they covalently bond with no free electrons
As you heat it up, some bonds start breaking which releases electrons
How do semiconductors conduct?
They are covalently bonded in a lattice structure. As temperature melts, more bonds break which releases electrons. So current increases with temperature increase
What is the number density of insulators?
Close to 0
Define mean drift velocity
The average velocity of charged particles
What is the formula for mean drift velocity?
I = ANEV
How is mean drift velocity like in conductors, semiconductors and insulators
In a conductor there is a large value of N so drift velocity is small even if there is a large current
In a semiconductor, N is slightly smaller so V is higher
An insulator has N close to 0 and current is not able to flow
What happens if cross sectional area halves?
Mean drift velocity doubles for the same current
