P15: Electromagnetism

What is the difference between a permanent and an induced magnet

A permanent magnet produces its own magnetic field, whereas an induced magnet becomes magnetic only when placed in a magnetic field and loses its magnetism when removed.

How do you plot a magnetic field using a compass

Place a compass near a magnet, mark the direction of the needle, move the compass to the new point, repeat across the area, and join the points with lines pointing north to south.

What is the magnetic field pattern around a straight current-carrying wire

It forms concentric circles centered on the wire, where field strength decreases as distance from the wire increases and direction depends on current direction.

How does a solenoid increase magnetic field strength

Coiling the wire creates a strong uniform magnetic field inside that resembles a bar magnet, which can be further strengthened by adding an iron core.

What is the motor effect

A current-carrying conductor placed inside a magnetic field experiences a force due to the interaction between its magnetic field and the external magnetic field.

How do you use Flemings left hand rule

Point your Thumb in the direction of Motion or force, First finger in the direction of the magnetic Field from north to south, and seCond finger in the direction of conventional Current.

How does a direct current electric motor keep rotating

Current flows through a coil in a magnetic field causing opposite forces on each side, and a split-ring commutator reverses the current direction every half turn to keep rotation continuous.

How does a loudspeaker convert electrical signals into sound waves

An alternating current passes through a coil attached to a speaker cone in a magnetic field, causing rapid changing magnetic forces that vibrate the cone to create sound waves.

What is the generator effect

Moving a conductor through a magnetic field or changing a magnetic field across a conductor induces a potential difference across its ends.

What is the difference between an alternator and a dynamo

An alternator uses slip rings to output an alternating current, while a dynamo uses a split-ring commutator to produce a direct current.

How does a microphone convert sound waves into electrical signals

Sound waves hit a flexible diaphragm attached to a coil, moving the coil through a magnetic field to induce an alternating potential difference with the same frequency.

How do step-up and step-down transformers work

A step-up transformer has more secondary turns to increase voltage and decrease current, while a step-down transformer has fewer secondary turns to decrease voltage and increase current.

How is power conserved across a transformer

Assuming 100 percent efficiency, the electrical power supplied to the primary coil equals the electrical power delivered by the secondary coil (primary potential difference times primary current equals secondary potential difference times secondary current).

Why are step-up transformers used in the National Grid

They increase voltage to lower current, which drastically reduces power lost as heat through wires during long-distance transmission.

What increases the magnitude of an induced potential difference

Increasing the speed of movement of the magnetic field, increasing the strength of the magnetic field, or increasing the number of turns on the coil.

How does the soft iron core in a transformer work

The alternating current in the primary coil creates a continuously changing magnetic field in the soft iron core, which easily magnetises and demagnetises to induce an alternating potential difference in the secondary coil.

What is the direction of an induced current

The induced current always flows in a direction such that its magnetic field opposes the original change in magnetic field that created it.

How does changing the speed of rotation affect an alternator trace

Increasing the rotation speed increases both the peak potential difference and the frequency of the alternating current output.

How does a transformer function only with alternating current

An alternating current creates a constantly changing magnetic field required to induce potential, whereas a constant direct current creates a static field that cannot induce potential.