Magnetism and Magnetic Effects: Fields, Forces, and Ferromagnetic Materials

Vocabulary-style flashcards covering key concepts from the notes on magnetic forces, fields, current loops, and ferromagnetism.

Magnetic force on a current-carrying wire

The force on a straight wire of length L carrying current I in a magnetic field B; magnitude F = I L × B; direction given by the right-hand rule.

Magnetic field from a long straight wire

Magnetic field B1 produced by a long wire with current I1 forms concentric circles; magnitude B1 = μ0 I1 /(2π r) and direction given by the right-hand rule.

Right-hand rule (forces on current-carrying wire)

Rule to determine force direction on a current-carrying wire: F = I L × B; use the right-hand rule to find the force direction.

Force between parallel wires (same direction)

A second wire with current I2 in the field of the first experiences a force; currents in the same direction attract.

Force between parallel wires (opposite direction)

If I2 is opposite to I1, the wires repel.

Force between current loops (same direction)

Two parallel current loops attract when the currents circulate in the same direction.

Force between current loops (opposite direction)

Two parallel current loops repel when the currents circulate in opposite directions.

Magnetic dipole moment (μ)

μ = I A, where I is the current and A is the loop area; a measure of the torque a loop experiences in a magnetic field.

Torque on a current loop in a uniform field

A current loop experiences torque τ = I A B sinθ (or μ × B); in a uniform field, net force is zero but a torque tends to align the loop with the field.

Uniform magnetic field

A magnetic field with constant magnitude and direction across the region; ensures equal and opposite forces on opposite sides of a loop, yielding a net torque but no net force.

Ferromagnetism

Strong attraction to magnets and the ability to be magnetized; due to unpaired electron magnetic moments aligning in materials.

Ferromagnetic material

Materials with net magnetic moments from unpaired electrons that can be magnetized; examples include Fe, Co, Ni and certain alloys, often containing magnetic domains.

Magnetic domains

Regions within a ferromagnet where atomic moments are aligned; domains tend to cancel externally, giving no net magnetization unless aligned.

Domain alignment under external field

External magnetic field causes domains aligned with the field to grow at the expense of opposing domains, producing a net induced moment.

Induced magnetic moment

Magnetic moment that develops when an external field aligns domains in a material.

Permanent magnet

A ferromagnetic material that remains magnetized even without an external magnetic field.

Magnetizing

Process of aligning domains in a ferromagnetic material by applying a strong external magnetic field to create a permanent magnet.

Magnetic poles

A ferromagnetic material has north and south poles and generates a magnetic field around it.

Cutting a magnet in half

Produces two magnets of half strength, each still possessing north and south poles.

Armature

The rotating coil in an electric motor where current flows to produce torque.

Commutator

Device that reverses the current in the loop every half cycle to keep the torque direction consistent (e.g., clockwise).

Torque in a motor (clockwise)

The force distribution on the loop in a motor leads to a clockwise torque, causing rotation.