charge and current Flashcards
Like charges….
Repel
Unlike charges…
Attract
describe net charge
The overall charge of an object
state the SI unit of charge.
A coulomb
what symbol represents charge?
Q
what symbol represents the unit of charge?
C
state the formula we can use to find the total charge of a number of particles
No of coulombs = Charge of 1 particle x No of particles
Define a free charge
A charge which isn’t bound to an atom or molecule and can move freely
Define number density
The number of free electrons per cubic metre
Silver has a very high number density. Is it a conductor or insulator?
Silver has a lattice structure with positive silver ions and many free electrons per cubic metre.
As a result, silver has a very high number density, therefore its a conductor
Diamond has a very low number density…
Therefore diamond is an insulator
describe a metal’s structure
Metals have a lattice structure made up of positive ions and free electrons.
why do electrons move so much in wire with no charge?
The delocalised electrons move due to the temperature of the wire. (even at room temperature)
Define thermal velocity
The movement of free charges due to temperature
Describe the average velocity of free charges in a wire (not connected to a power source)
The average velocity of the free charges in the wire is zero.
This is because the free charges move randomly.
We can assume the total charge at any point is constant
describe why the average velocity of free charges in a wire is 0
Velocity is a vector quantity. The motion of free electrons due to their thermal energy is random.
on average equal numbers of electrons move in every direction.
there is no net movement of free electrons
state the symbol that represents current
I
Define current
The rate of flow of charge
State the units of current
Ampere (A)
1 amp = 1 coulomb per second
The number of coulombs moving past a given point per second…
Is called a current
adding a power source to a circuit causes
The free electrons to drift towards the positive terminal
There’s a constant amount of electrons moving…
Into the battery and out of the battery
describe what happens to the electrons when a power source is connected.
The free electrons in the wire drift because they are pulled towards the positive terminal and pushed away from the negative terminal
the battery dies when…
All the reactants are used up.
work out the current if 3 coulombs of charge pass a point each second.
3 AMPS
what is an ammeter?
An ammeter is a device that measures the current in a circuit
What is an ammeter used for?
Ammeters are used for measing the current in a circuit
An ideal ammeter…
Will not affect the current in the circuit
State the direction of conventional current
Always in the opposite direction of negative charges.
Always matches the direction of the drift of positive charges
