7 - Magnetism and Electromagnetism

• Alternator: A device that makes use of the generator effect to generate alternating current
• Attraction: Opposite poles will experience a force of attraction, meaning they will experience a force towards each other
• The force between a magnet and magnetic material is always one of attraction
• Current-Carrying Wires: When current flows through a wire, a magnetic field is generated around it
• The strength of the field is dependent on the magnitude of the current and the distance from the wire
• Dynamo: A device that makes use of the generator effect to generate direct current
• Electric Motor: A current-carrying coil of wire in a magnetic field
• The two sides of the coil that are perpendicular to the magnetic field experience forces in opposite directions, causing rotation
• Electromagnet: A solenoid with an iron core
• Fleming’s Left-Hand Rule: A rule used to determine the orientation of the force (thumb), current (second finger) and magnetic field (first finger) when a current-carrying wire is placed in a magnetic field (motor effect)
• Generator Effect: When there is relative motion between an electrical conductor and a magnetic field, a potential difference will be induced across the ends of the conductor
• A current will flow if this conductor is part of a complete circuit
• Induced Magnet: A material that becomes a magnet when it is placed in an existing magnetic field, but loses its magnetism quickly once it is removed
• Induced magnetism always produces attractive forces
• Magnetic Compass: A device containing a small bar magnet that points in the direction of the Earth’s magnetic field
• Magnetic Field Lines: Lines representing the strength and direction of a magnetic field
• North and South Poles of magnets repel each other.
• The field line direction at any point is in the direction that a force would act on another north pole if placed at that point
• Opposite poles of magnets attract each other.
• Permanent magnets are always magnetic and always have poles.
• Magnetic Field: The region around a magnet in which another magnet or magnetic material will experience a force
• Magnetic Materials: Iron, steel, cobalt and nickel
• Induced magnets are materials that are “magnetic” but do not have fixed poles.
• Induced magnets can be made into temporary magnets by stroking them with a permanent magnet.
• Magnetic Poles: The regions of a magnet where the magnetic forces are at their strongest
• Induced magnets align the domains in the material all in the same direction, creating a temporary magnet.
• Microphone: A device that uses the generator effect to convert the pressure variations of sound waves into variations in the electrical current of a circuit
• Iron, Nickel, Cobalt are magnetic materials.
• Field Lines in a magnetic field point from North to South.
• Motor Effect: When a current-carrying wire is placed in a magnetic field, a force will be experienced between the wire and the magnet responsible for the field
• The strength of a magnetic field decreases with distance from the magnet.
• The magnetic field from the magnet and from the current interact, causing the coil to move.
• A fixed magnet is at the centre, and the coil of wire around the magnet is free to move.
• Pressure variations in the sound waves cause the coil to move, and as it moves current is induced in the coil (because it cuts the magnetic field).
• The current is then sent to a loudspeaker.
• Dynamic microphones produce a current which is proportional to the sound signal.
• The cone of the loudspeaker moves, producing pressure variations, making sound.
• The setup for loudspeakers is identical, working in reverse.
• The current flows into the coil.
• Step down transformers are used to reduce voltage.