6. Electromagnetism: Motors, Generators, and Transformers

Electricity and magnetism are two faces of the same force — electromagnetism. Each one can create the other.

Electricity → Magnetism (electromagnets):
Any wire carrying current produces a magnetic field around it. Coiling the wire into a solenoid concentrates and strengthens the field, making an electromagnet. Key properties:

• Strength increases with more coils or higher current.
• The magnetism turns on and off with the current — unlike a permanent magnet.
• Used in: MRI machines, electric motors, speakers, doorbells, cranes.

Magnetism → Electricity (electromagnetic induction):
Moving a conductor through a magnetic field (or moving a magnet near a conductor) induces a voltage in the wire — discovered by Michael Faraday. This is the principle behind generators.

[missing figure: generator]

Electric motors do the reverse: a current-carrying coil placed in a magnetic field experiences a force that makes it rotate — converting electrical energy → mechanical energy (motion).

Transformers use electromagnetic induction to change voltage levels in AC (alternating current) circuits:
\[ \frac{V_{\text{primary}}}{V_{\text{secondary}}} = \frac{N_{\text{primary}}}{N_{\text{secondary}}} \]
where \(N\) is the number of coil turns.

• Step-up transformer: more secondary turns → higher output voltage (used to send electricity long distances at high voltage and low current to reduce energy loss).
• Step-down transformer: fewer secondary turns → lower output voltage (used near homes to bring voltage down to safe levels).