Electromagnetic effects

Electromagnetic Induction

Process where an electromotive force (e.m.f.) is induced in a conductor when there is relative movement between the conductor and a magnetic field.

Two ways to induce e.m.f.

1. Conductor moves in a stationary magnetic field. 2. Conductor is stationary in a changing magnetic field.

Lenz's Law

The direction of an induced e.m.f. always opposes the change causing it.

Right-hand dynamo rule

Used for direction of induced e.m.f.: First finger = Field

Factors increasing induced e.m.f.

Speed of movement

A.C. Generator

Device that converts mechanical energy to electrical energy

Components of A.C. generator

Permanent magnet (uniform field)

When is e.m.f. maximum in A.C. generator?

When coil is horizontal and moving perpendicular to magnetic field.

When is e.m.f. zero in A.C. generator?

When coil is vertical and moving parallel to magnetic field.

Right-hand grip rule for straight wire

Thumb points in current direction; curled fingers show magnetic field direction.

Solenoid magnetic field

Similar to a bar magnet; field lines emerge from north pole and return to south pole.

Factors strengthening solenoid field

Increase current

Electromagnet

Solenoid with soft iron core; becomes magnetic when current flows.

Fleming’s left-hand rule

Thumb = Force

Charged particle in magnetic field

Deflected if moving perpendicular to field lines; force direction found via Fleming’s rule (reverse for electrons).

D.C. Motor

Converts electrical energy to mechanical energy using the motor effect; coil rotates continuously.

When does coil experience max force in D.C. motor?

When coil is horizontal and perpendicular to magnetic field.

Factors increasing D.C. motor speed

Increase current

Transformer

Device that changes size of alternating voltage/current using primary and secondary coils on iron core.

Step-up transformer

Increases voltage; has more turns on secondary coil than primary (Ns > Np).

Step-down transformer

Decreases voltage; has fewer turns on secondary coil than primary (Ns < Np).

Operation of transformer

A.C. in primary coil creates changing magnetic field in iron core

High-voltage transmission purpose

Reduces current (P = VI)

Role of step-up transformer in grid

Increases voltage at power station for efficient long-distance transmission.

Role of step-down transformer in grid

Decreases voltage to safe levels (e.g.

Power loss formula

P_loss = I² × R; loss increases with current squared.

Right-hand dynamo rule vs. Left-hand rule

Right-hand: for generators (induced current). Left-hand: for motors (force on conductor).

A.C. vs. D.C. generator

A.C. uses slip rings; D.C. uses split-ring commutator to produce direct current.

Solenoid vs. Bar magnet field

Identical pattern