Chapter 22 Magnetism & Chapter 23 Electromagnetism (Exam 3)

Magnet

Object with a north and south pole that produces a magnetic fieldObject with a north and south pole that produces a magnetic field

Magnetic Poles

North and south ends of a magnet; like poles repel, opposite poles attract.

Magnetic Monopole

Does NOT exist; poles always come in pairs

Earth’s Magnetic Field

Acts like a giant magnet; geographic north is actually a magnetic south pole

Magnetic Field

Region around a magnet or current where magnetic forces act

Magnetic Field Lines

Lines showing direction and strength of the field (denser = stronger)

Rules of Magnetic Field Lines

Go from north → south outside magnet

Form closed loops

Never cross

Conditions for Magnetic Force

Charge must be moving

Velocity must have a perpendicular component to B

Lorentz Force

Magnetic force on a charge.

Right-Hand Rule #1 (Force)

Thumb = velocity

Fingers = magnetic field

Palm = force (positive charge)

Right-Hand Rule #2 (Wire Field)

Thumb = current

Fingers = magnetic field direction

Circular Motion of Charge

Magnetic force acts as centripetal force → circular path.

Hall Effect

Voltage produced across a conductor in a magnetic field.

Purpose of Hall effect

Determines charge type (positive vs negative)

Measures fluid flow (like blood)

Force on Current-Carrying Wire

Magnetic field exerts force on moving charges in wire

Torque on Current Loop

Magnetic forces cause rotation

Motor

Converts electrical energy → mechanical energy

Long Straight Wire Field

Circular field lines around wire

Ampere’s Law

Relates magnetic field to current producing it

Solenoid

Coil producing strong, uniform magnetic field

Parallel Wires

Same Direction Currents → Attract

Opposite Direction Currents → Repel

Magnetic Flux

Magnetic Flux (Φ)
Amount of magnetic field passing through an area.

Φ=BAcosθ

Electromagnetic Induction

Process of generating emf by changing magnetic flux

Faraday’s Law

Induced emf is proportional to change in flux.

E=−dtdΦ

Lenz’s Law

Induced current opposes the change in magnetic flux

Motional EMF

Voltage generated when conductor moves in magnetic field

Generator

Converts mechanical energy → electrical energy using rotating coils

Transformer

Changes AC voltage levels

Step-Up Transformer

Increases voltage, decreases current

Step-Down Transformer

Decreases voltage, increases current

Mutual Inductance

One coil induces emf in another

Self-Inductance

Coil induces emf in itself when current changes

Inductor

Device that stores energy in magnetic field.

Energy in Inductor

E=1/2LI^2

Time Constant (τ)

Time for current to rise or decay.

τ=R/L

Current Growth (Charging)

Starts at 0 → approaches max

Induced emf increases when

Magnetic field increases

Area increases

Angle changes

Speed increases

What happens when magnetic flux increases?

→ Induced current opposes increase (Lenz’s Law)

What determines direction of induced current?

→ Lenz’s Law + Right-Hand Rule

What increases generator output?

→ More loops, stronger B-field, faster rotation

What happens in a step-up transformer?

→ Voltage ↑, Current ↓

What is required for magnetic force?

→ Moving charge + perpendicular velocity