1. Conduction of electricity Flashcards
Difference between vector and scalar?
Vector = magnitude and direction
Scalar = magnitude only
Define electric current (I)
A flow of charge
Define electric charge (Q)
current x time, measured on Coulombs
An electron has a charge of 1.6x10^-19C
(ofc in data booklet but mehhh, first principles)
Define coulomb (C)
1C = total charge supplied by a current of 1A in a time of 1s
Equation for number of electrons in a wire?
Total charge in circuit/Charge of an electron
Which direction is convectional current?
Positive (+) –> Negative (-)
But how do we know electron flow is negative –> positive?
- Current is the flow of negative free electrons
- Positive metal ions don’t move
What is drift velocity?
The average speed at which electrons travel in a conductor when subjected in an electric field
When a current is applied the electrons still move randomly but tend to move in one direction
How to derive drift velocity
step 1
From diagram of wire 3D shape:
- Gain area = A
- Gain drift velocity = V
- Gain time = t
- Gain number of free electrons = n
How to derive drift velocity
step 2
Gain length:
v x t = L
How to derive drift velocity
step 3
Gain volume:
A x L = Avt
How to derive drift velocity
step 4
Number of electrons:
nAvt
How to derive drift velocity
step 5
Gain total charge:
Q = nAvte
How to derive drift velocity
step 6
Re-arrange for current:
Q/t = nAve
Q/t = current O_o
How to derive drift velocity
step 7
Gain current:
I = nAve
Let it rest
