10. Magnetism (2nd exam)

What is magnetism?

a fundamental force tied to electricity that originates from the motion of electric charges

What are lodestones?

• Naturally magnetized pieces of the mineral magnetite.

• First known magnetic materials.

• Attract iron and align with Earth’s magnetic field

What’s a compass?

A small, lightweight indicator that aligns with magnetic fields.

What are diamagnetic materials?

nonmagnetic materials

What are paramagnetic materials?

materials are weakly attracted to a magnet. also referred to as nonmagnetic

What are ferromagnetic materials?

these are materials such as magnetite. they produce a “permanent magnet”

What’s a permanent magnet?

• a material that produces a magnetic field without the need for an external power source.

• The key feature of permanent magnets is the magnetic domains.

What are magnetic domains?

• Regions within a material where groups of atoms have their magnetic moments aligned in the same direction.

• Unmagnetized = domains are random

• Magnetized = Domains align, creating a strong field.

The direction of the magnetic field in a permanent magnet is conventionally defined as from the ___ pole (where the magnetic field lines exit the magnet) to the ___ pole (where the magnetic field lines enter). The magnetic field forms a ___ loop outside the magnet.

1. North pole

2. South pole

3. Continuous

What happens outside of the magnet?

The magnetic field lines exit from the north pole and curve around to enter the south pole.

What happens inside of the magnet?

The field lines travel from the south pole to the north pole

What are field line directions?

Direction of the field is given by the direction a compass points.

Opposite poles ___, and like poles ___

attract (North + South), repel (North + North)

Breaking a magnet in half…

doesn’t separate the poles

What’s the difference between magnetic and magnetized?

Magnetic = Influenced by/attracted to a magnet. (Example A steel nail or paper clip.)

Magnetized = Magnetic domains are aligned to provide a large net field to make the object a magnet.

___ generates magnetic fields. It’s field strength is ___ to current.

electric current, proportional

For a moving charge:

The direction of the magnetic field is found by the right-hand rule. Point your thumb in the direction the charge is moving (velocity), and curl your fingers. Your fingers curl in the direction of the magnetic field.

For a Current-Carrying Wire:

The magnetic field around a straight current-carrying wire forms concentric circles. The direction of the magnetic field is determined by the right-hand rule: If you point your thumb in the direction of the current, your fingers will curl around the wire in the direction of the magnetic field.

For a Coil of Wire (Solenoid):

It creates a magnetic field similar to that of a bar magnet, with distinct north and south poles.

The field's polarity is determined by the right-hand rule: by curling your fingers in the direction of the current, your thumb will point directly to the north pole.

Electromagnets:

Magnetic field created by electric current.

• Wire + ferromagnetic core.

Electric motors:

• Convert electrical energy to mechanical energy

1. Coil in magnetic field

2. Current creates magnetic field

3. Interaction causes rotation

What does a commutator do in electric motors?

Reverses current for continuous motion.

Speakers:

Convert electrical signals to sound.

• Coil moves, diaphragm vibrates → sound waves.

What’s Electromagnetic Induction?

Changing magnetic field induces voltage.

• Faraday’s Law: Voltage is proportional to the rate of change of magnetic flux.

• Basis for generators, transformers, wireless charging.

Generators:

Convert mechanical energy to electrical energy.

• Produces AC or DC depending on design.

Microphones:

Convert sound waves to electrical signals.

• Vibrates with sound.

• Induced current mirrors sound wave.

Inductive charging:

Wireless energy transfer via magnetic fields.

• The primary coil is in the charger (creating a magnetic field), while the secondary coil is in the device (receives energy).

Regenerative Braking:

Used in electric vehicles.

1. Motor becomes generator during braking.

2. Converts kinetic energy to electrical energy.

3. Stores energy in battery.

4. Reduces brake wear.

What’s the purpose of transformers, and where do they apply?

Change the voltage of alternating current (AC).

They are applied in power distribution, electronics, and chargers.

What are the types of transformers?

• Step-Up Transformer: Increases voltage.

• Step-Down Transformer: Decreases voltage.

How do transformers work?

• Two coils (primary and secondary) wrapped around a shared iron core.

• AC in the primary coil creates a changing magnetic field.

• This field induces a current in the secondary coil.

What’s Faraday’s Law?

Voltage is proportional to the rate of change of magnetic flux