magnetism & Electromagnetism

• The wire is along the y-axis, where current is moving up from C to D.
• The movement of the wire causes the wire to produce an electromotive force, which is used to power an external circuit.
• In an electric motor, permanent magnets lie in fixed positions, with a coil of current-carrying wire lying on an axis.
• A current flows if the conductor forms a complete circuit, which will produce its own magnetic field, which opposes the change inducing it.
• When current flows in one direction, the force on one side moves that side up, while the force on the other side moves down.
• A turbine spins turning the coil of wire, causing the wire to rotate.
• Two magnets will interact, feeling a magnetic force of attraction/repulsion.
• Along the z-axis, Fleming’s Left Hand Rule is used to determine the unknown factor out of the three (usually the direction of the force felt).
• A magnet and a wire will also exert a force, as the two magnetic fields generated by the magnet and the current in the wire will interact.
• Magnetic Flux Density is measured in Tesla and is the number of flux lines per metre squared.
• Current is conventional current, which moves in opposite direction to the electrons.
• When there is a relative movement between a conductor and a magnetic field, a potential difference is induced across the conductor.
• The force felt on the wire is at right angle to both the direction of the current and magnetic field lines.
• In an electric generator (dynamo), the same setup as a motor is used, with a coil of wire able to rotate between two permanent magnets.
• The magnetic field around a wire is circular, but the magnetic field between two magnets is straight.
• Fixed permanent magnets have field lines along the x-axis, as the magnets are at A and B and the field lines are shown.
• When two interact, the wire is pushed away from the field between the poles (at right angles to the wire direction and the field direction).
• North and South Poles of magnets repel each other.
• Opposite poles of magnets attract each other.
• Permanent magnets are always magnetic and always have poles.
• Induced magnets are materials that are “magnetic” but do not have fixed poles.
• These can be made into temporary magnets by ‘stroking’ them with a permanent magnet.
• Producing pressure variations, making sound
• The magnetic field lines point from North to South.
• The strength of a magnetic field decreases with distance from the magnet.
• The direction of a magnetic field always points to the south pole and away from the north pole, at any point.
• Plotting compasses on a piece of paper through which a wire is pierced shows the direction of the magnetic field.
• The core of the Earth is magnetic and creates a large magnetic field around the Earth.
• A freely suspended magnetic compass will align itself with the earth’s field lines and point North.
• The compass is effectively a suspended Bar Magnet, with its own north pole lining up with Earth’s ‘North pole’.
• Earth’s magnetic pole above Canada is a magnetic South Pole and the geographic south pole is close to the Magnetic North Pole.
• Current produces a magnetic field around the wire, with the direction dictated by the “right hand grip rule”.
• The strength of a magnetic field increases with greater current and decreases with greater distance from the wire.
• The Motor Effect is the phenomenon where a current-carrying wire experiences a magnetic force.
• A change in magnetic field creates a potential difference, which can be used to power an alternating current (AC) or a dynamo.
• 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).
• More coils on the secondary of a transformer will increase the voltage, as the changing field will cut through more of the secondary wire inducing a larger potential difference.
• The current produced by a dynamic microphone is then sent to a loudspeaker.
• The magnetic field from the magnet and from the current interact, causing the coil to move, causing the cone to move.
• Dynamic microphones produce a current which is proportional to the sound signal, with a fixed magnet at the centre and the coil of wire around the magnet is free to move.