Current and charge
Electric current is a flow of electrical charge.
In a metal the the electrical current is due to the conduction electrons (otherwise known as Free electrons at GCSE). The coduction electrons are not 'bonded' to the nucleous of the atom and therefore free to move to other shells. This movement is current of electricity.
In electorlyte this is different. Electric current is due to ions (charged atoms). These Ions can be negitively or positively charged. the Negitively charged particles will gravitate to the Cathode (positively charged rods that attract the oppersite charged ions). Positively charged ions will gravitate to the Anode, which is negitively charged.
Conventional current - conventional current is the movement of electrons form the positive terminal to the negitave terminal of a cell or battery.
Electron flow - An electron flow is the oppersite direction to the conventional current. It flows from the negitive terminal to the positive terminal of a cell or battery.
They are oppersite becasue when convetional current moves around it displaces an electron. Imagine a round desk of 10 people, but there are 11 seats. This seat is the positively charged atom. When a person (an electron) moves to move the space forward the electron dispalaces. This is how they are in oppersite directions.
Charge is measured in coulombs and is defined by current x time
I = Q x t
which is measured in coulomps (C), Amps (A) and Seconds (S) respectively.
One number you will need to know is the elimentry charge on an electron, which is e= 1.6 x 10 to the power of -19 C. This will be used in drift velocity and other equations that require you to know the charge of one particel.
I talked earlier about current and I failed to mention one thing, Ameatres.
Current can be measured in amps which can be measured in a curcit with an amp metre. This is put in series with the curcit and has neible resistance so you dont have to inculde it when calculating relistance, unless asked for.
Kirchhoff's First law
Kirchhoff was a physist (duh) that you will come up accross qiute a lot. so remember him and dont forget what he said.
First law - The sum of the currents entering a junction is always the same as the current leaving a junction.
This is a result of conservation of charge. The amount of energy input has not change and neither has the resistace so the current will not chage. Current can not be lost either, It neaver leaves the curcit, is a prisoner to it.
Mean Drift Velocity
Mean drift velocity - The average velocity of an electron in a wire due to the potentioal dirfferance through it.
This is eaily reprosented by I=nAve
Current (I), number of lectrons (n), cross-sectional area (A), drift velocity (v) and the elermentary charge (e) which you will remeber as 1.6 x 10 to the power of -19.
Number desity of electrons chages depending on the material.
Conductors have a high number density so have a higher drift velocity and therefore a higher conductivity.
Insulators have low number dencity, so they have fewer conduction electrons and a smaller dirft velocity making them not very conductive.
Semi-conductors are a mix between both. However the drift velocity can be chaged by adding imperieties.