Charge and current Flashcards
Define electric current
The rate of flow of charge.
What is one ampere?
One coulomb of charge passing through a given point per second
How do you find the net charge?
Q=+/-ne
N is the number of electrons
What does it mean when charge is quantised?
Charge can only take certain values- multiple of e
What experiment was used to determine the amount of charge on an electron?
The oil drop experiment
What are charge carriers in metals?
Electrons
What are charge carriers in liquids?
Ions
What is the structure of a metal?
A lattice of positive ion surrounded by delocalised electrons.
Positive ions aren’t free move they only vibrate around a fixed point.
How do you produce a higher current?
- Add more electrons to pass a given point per second
2.Make the same number of electrons pass but at a faster rate.
What is conventional current?
Current is the positive ions moving from the positive terminal toward the negative.
What is the direction of electron flow?
It is always opposite the conventional currents- negative terminal to positive terminal.
What are liquids that carry electrical current called?
Electrolytes
What is the ideal ammeter?
Zero resistance so it has no affect on the current
State the conservation of charge
Charge can neither be created or destroyed only transferred.
What is Kirchhoff’s first law?
The sum of currents into a junction is equal to the sum of currents leaving the junctions.
When is current positive?
When current is going towards the junctions ‘in’
When is current negative?
When current is going away from the junction ‘out’
What is the sun of current equal to according to Kirchhoff first law?
Sum of currents=0
What is number density?
The number of free electrons per cubic meter of a material
The higher the number density….
The more free electrons- the greater of an electrical conductor.
What is the number density of conductors?
10^28
What is the number density of semiconductor?
10^17
What do semiconductor have to do to be as good as metals?
They need to carry the same amount of current so the electrons move faster and so the temperature of the semiconductor increase.
What is mean drift velocity?
The mean velocity of charges along the length of the conductor.
What is 12kA equal to?
12000 coulombs per second
In metals what is the electric current?
The flow of electrons
