p7 magnetism and electromagnetism

• repulsive : like poles repel
• attractive : opposite poles attract
• a current carrying wire induces a magnetic field around it
• an induced magnet becomes magnetic when placed in a field
• a permanent magnet produces its own magnetic field
• a compass points in the direction of earths magnetic north
• rotating a coil of wire through a magnetic field generates a current
• magnetic materials: iron, steel, cobalt and nickel
• solenoid is a coil of wire with a current flowing through it
• flemings left hand rule: For a current carrying conductor at right-angles to a field
• Thumb: Force | Index Finger: Field | Middle Finger: Current
• if 100% efficient, input power = output power
• alternator = generates alternating current
• dynamo = generates direct current
• transformers consist of a metal core with a primary coil of wire on one side and a secondary coil of wire on other side
• Power lines carry current at a very high voltage, to reduce the current, which improves efficiency by reducing the energy loss through heating
• change direction of the force : reverse the direction of the current, reverse the poles of the magnet
• size of force is determined by length of wire, size of current and strength of magnet (flux density)