2.3 Magnetism and Electromagnetism

North and South Poles

Same Poles repel; Opposite poles attract.

Permanent Magnets

Always magnetic, always have poles.

Induced Magnets

Materials that are 'magnetic' but do not have fixed poles; These can be made into temporary magnets by 'stroking' them with a permanent magnet.

Temporary Magnet Creation

Aligns the domains in the material all in the same direction, creating a temporary magnet.

Materials for Induced Magnets

Iron, Nickel, Cobalt.

Magnetic Fields

Field Lines point from North to South; Strength decreases with distance from the magnet.

Direction of Magnetic Field

Direction always points to south pole and away from north pole, at any point.

Plotting Compasses

Small compasses which show the direction of the magnetic field at a certain point.

Earth's Core

The core is magnetic, and creates a large magnetic field around the Earth.

Compass Alignment

A freely suspended magnetic compass will align itself with the earth's field lines and point North.

Geographic North Pole

The compass does not point to the Geographic North pole - it is over North Canada.

Suspended Bar Magnet

The compass is effectively a suspended Bar Magnet, with its own north pole lining up with Earth's 'North pole'.

Like Poles Repel

This cannot be right, as like poles repel.

Earth's Magnetic Pole

Earth's magnetic pole above Canada is a magnetic South Pole.

Current

Current produces a magnetic field around the wire.

Right Hand Grip Rule

The direction of the magnetic field around a wire is dictated by the right hand grip rule.

Strength of Magnetic Field

Greater current results in a stronger magnetic field, while greater distance from the wire results in a weaker field.

Solenoid

A solenoid has a magnetic field shape similar to a bar magnet and enhances the magnetic effect by aligning the field.

Iron Core

Having an iron core in the center of a solenoid increases its strength as magnetic field lines pass through it more easily than air.

Factors affecting strength of solenoid

Factors include size of current, length, cross-sectional area, number of turns (coils), and using a soft iron core.

Motor Effect

The motor effect occurs when two magnets interact, exerting a magnetic force of attraction or repulsion.

Magnetic Field around a Wire

The magnetic field around a wire is circular, while the magnetic field between two magnets is straight.

Force on Wire

When a wire interacts with a magnetic field, it is pushed away from the field at right angles to both the wire direction and the field direction.

Fleming's Left Hand Rule

Fleming's Left Hand Rule helps determine the unknown factor out of the three directions, usually the direction of the force felt.

Conventional Current

Conventional current moves in the opposite direction to the electrons.

Magnetic Flux Density

Magnetic Flux Density is measured in Tesla and represents the number of flux lines per meter squared.

Electric Motors

Electric motors use a coil of current-carrying wire between fixed permanent magnets to create rotational motion.

Force on Coil

The force on one side of the coil moves it up, while the force on the other side moves it down, causing rotation.

Electromagnetic Induction

Electromagnetic induction occurs when there is relative movement between a conductor and a magnetic field, inducing a potential difference across the conductor.

Complete Circuit

A current flows if the conductor forms a complete circuit.

Electric Generator (Dynamo)

A device that produces direct current (DC) by reversing the current each half-rotation using a split ring commutator.

Alternating Current (AC)

An electric current that reverses direction periodically, produced by an alternator.

Potential Difference

The difference in electric potential energy per unit charge between two points in a circuit.

Step Up Transformer

A transformer that increases voltage by having more coils on the secondary side.

Step Down Transformer

A transformer that decreases voltage by having fewer coils on the secondary side.

Dynamic Microphone

A type of microphone that produces a current proportional to the sound signal, using a moving coil in a magnetic field.

Loudspeaker

A device that converts electrical energy into sound, using a coil that moves in a magnetic field.

Turbine

A device that spins to turn a coil of wire in a generator, inducing an electric current.

Magnetic Field

A field around a magnet where magnetic forces can be observed, crucial for the operation of generators and transformers.

Induction

The process by which a changing magnetic field induces an electric current in a conductor.

Coil of Wire

A wire wound in a spiral shape, used in generators and transformers to create magnetic fields.

Split Ring Commutator

A device used in dynamos to reverse the direction of current in the coil, ensuring a constant output.

Changing Magnetic Field

A magnetic field that varies over time, necessary for inducing current in transformers.

Efficiency of Transformer

The ratio of output power to input power, ideally 100% but often less in practice.

Pressure Variations

Changes in air pressure caused by sound waves, which induce movement in microphones and loudspeakers.

Induced Current

The electric current generated in a conductor due to its motion through a magnetic field.

Magnetic Field Interaction

The interaction between magnetic fields from a magnet and current, causing movement in devices like loudspeakers.

AC in First Coil

The alternating current that creates a changing magnetic field in the primary coil of a transformer.