Electricity & Magnetism

• Magnetism describes the ability of magnets to attract or repel other magnets without touching them
• Magnets have a north and south pole
• Opposite poles attract
• Like poles repel
• Magnetic forces are caused by magnetic fields
• When the magnetic fields of two magnets overlap, it causes the magnets to pull or push each other
• Iron, nickel and cobalt are the only pure metals that can be turned into magnets
• Magnetic materials don't always act like magnets but they can be attracted to another magnet if they are close enough
• Magnetic materials can only be attracted by a magnet
• Only magnets can repel each other
• Permanent magnets are always magnets even when they're not interacting with other magnets
• Induced magnetism is when a magnetic material will temporarily become a magnet when close to a permanent magnet
• The permanent magnet induces poles in the magnet material so that they align. Example: If the north pole of the permanent magnet is close to the magnetic material, a south pole will be induced
• When the permanent magnet moves away from the magnetic material, it loses its induced polarity
• Magnetic materials can be turned into permanent magnets by stroking, hammering or solenoid and direct current
• Stroking involves rubbing two different metals together repeatedly until one becomes attracted to the other
• Solenoids involve wrapping wire around an iron rod and passing a current through it which creates a strong magnetic field inside the coil
• Hammering is when you put the magnetic material in a strong magnetic field and hit with a hammer many times
• Demagnetisation can happen by heating the magnet, by passing AC through the coil or hitting the magnet when it's not in a strong magnetic field
• An electromagnet is made from a cylindrical coil of wire that has an electric current passing through it
• An electromagnet is only magnetic when there is a current passing through it
• Permanent magnets are usually made from steel or other magnetically hard alloys
• To increase the strength of an electromagnet you can add an iron core, increase the electric current or increase the number of coils of the wire
• Charge is measured in Coulombs (C)
• When there is a difference in positive and negative charge between two objects, there is a potential difference. The p.d causes a rapid transfer of charge, which is known as 'static' electricity. This causes a spark
• Charged objects can exert force on each other
• Rubbing two objects together causes electrons to jump from one object to another - causing both objects to become charged
• A charged object moved close to an uncharged object can induce (cause) charges in the uncharged object. This is called charging by induction.
• Direction of electric field is away from the positive ion
• Electrical current is the flow (movement) of electric charges.
• Current is measured in Amperes (A)
• All metals are electrical conductors
• Insulators are plastic and glass
• Semi-conductors are germanium and silicon
• The electromotive force (e.m.f.) is a measure of the amount of energy an energy source supplies to each charge passing through it.
• Electromotive force is measured in volts (V)
• Potential difference is the difference in the amount of energy that charge carriers have between two points in a circuit.
• Resistance is a measure of how difficult it is for current to flow through a component.
• Resistances can be calculated using Ohms law, which states that voltage = current x resistance
• Size of current and resistance are inversely proportional