Physics P4

• Magnets have a north and south pole
• Between two magnets, like poles repel and opposite poles attract
• Permanent magnets are always magnetic and always have poles
• Induced magnets can be produced from materials that are magnetic but do not have fixed poles
• Iron, Nickel, and Cobalt are common induced magnetic materials
• Magnetic fields are shown using field lines that point from north to south
• The strength of the magnetic field decreases as distance from the magnet increases
• Small plotting compasses can be used to plot the shape of a magnetic field around a small magnetised object
• The Earth's core is magnetic and currents within it create a large magnetic field around the Earth
• A freely suspended magnetic compass aligns itself with the Earth's field lines and points North
• Current flowing in a wire produces a magnetic field around the wire
• The direction of the magnetic field around a wire is dictated by the 'right hand grip rule'
• Solenoids are formed from a coil of wire with current flowing through
• Factors affecting the strength of the magnetic field produced by a solenoid include: size of current, length of coil, cross-sectional area, number of turns (coils), and type of core used
• Two magnets will interact, feeling a magnetic force of attraction or repulsion
• Fleming's Left-Hand Rule can be used to find the direction of the force between a magnet and a wire
• An electric motor can be made using permanent magnets and a coil of current-carrying wire that rotates due to induced forces
• A conductor forms a potential difference as electrons move within it due to a change in the magnetic field
• Electric generators work by rotating a coil of wire between two permanent magnets to induce a potential difference and produce an alternating current
• Alternating current constantly changes direction, producing a changing magnetic field
• Transformers work by inducing a current in a secondary coil through a changing magnetic field created by an alternating current in the primary coil
• If there are more turns on the secondary coil, a step-up transformer is produced, increasing voltage
• If there are fewer turns on the secondary coil, a step-down transformer is produced, decreasing voltage
• Dynamic microphones produce a current proportional to the sound signal by inducing current in a coil of wire that moves within a fixed magnet