P5: Electricity and magnetism

Phenomena of magnetism

Opposites forces attract each other
Like forces repel each other
Magnetic materials (not magnets) stick to either side of a magnet
This is called induced magnetism, where magnetic objects become magnets and are attracted when next to permanent magnets (not repelled)

Magnetic Properties of soft iron and steel

Iron that can easily be magnetised and demagnetised
It is an induced magnet which becomes magnetised when it is near a magnet and placed in a magnetic field
Soft iron fillings can quickly lose and gain magnetism when near a magnet

A permanent magnet that always has a force on other magnets, as it creates its permanent magnetic field

Design of permanent magnets and electromagnets

A permanent magnet is a material that is permanently magnetised and creates its own magnetic field
Electromagnets are made from wire that allow an electric current to pass through to act as a magnet
However, a permanent magnet does not need an electric current

Electrical quantities

Electrical Charge

There are positive and negative electrical charges
Positive and negative charges attract each other, while the positive-positive or negative-negative repel each other
Insulators can be given a charge through friction

Insulators can be rubbed against an object to gain or lose electrons
When two objects are rubbed against each other, electrons can be transferred from a material to another, causing one object to be negatively charged, and the other to be positively charged
An object becomes charged when electrons are added or removed from an object
You could rub insulator rods against a cloth, and they will gain a charge
You can try this on two objects and observe whether the charges are like or opposite by seeing if they repel or attract each other

An electric field is a region where other charged objects are affected by an object with a charge
Conductors are materials that can transmit electricity well, while insulators are materials that transmit electricity poorly
Conductors often have a free flow of electrons, and include materials such as metals
Insulators often do not contain free electrons, meaning that they are bad at conducting electricity. They include materials suchas plastic and rubber

Current, potential difference, and electromotive force

An electric current is a flow of charged particles in one direction
The current is equal to the amount of charge that passes a point in a circuit per second
Current is travelled by an ammeter
Potential difference is the difference of the amount of electricity in two points in a circuit, and shows the amount of energy transferred from one point to another
The electromotive force is the energy provided by each coloumb of charge that goes through the power supply
Voltage is the unit of potential difference and electromotive force, which is equivalent to joule (energy) per coulomb (electric charge)
Potential difference can be measured by a voltmeter connected to two points in the circuit

Resistance

Resistance acts against a current and makes it lower
The formula to work out resistance is voltage/current
The longer wires are, the more resistance it will have, as there will be more collissions of electrons with the metal ions that conduct the electricity.
When a wire is thicker, the electrons collide less as there is more space for the electrons
The resistance and length is proportional, and when the length of a wire is increased by double, so will the resistance
The resistance of a wire is also inversely proportional to the thickness of the wire (cross-sectional area), and when the cross-sectional area of the wire is doubled, the resistance of the wire will decrease by half