Physics Lecture Review: Magnetic Forces to DC Circuits

Vocabulary-style flashcards covering magnetic forces, field sources, induction, LC oscillations, and DC circuit rules based on lecture notes.

Magnetic Force and Velocity Relationship

The magnetic force is always perpendicular to the particle’s velocity.

Magnetic Force and Magnetic Field Relationship

The magnetic force is always perpendicular to the magnetic field.

Work done by a Magnetic Field

A magnetic field does no work on a moving charged particle because the force is always perpendicular to the velocity, changing only direction and not speed or kinetic energy.

Conditions for Zero Magnetic Force

The magnetic force is zero if the particle is stationary ($v=0$), the magnetic field is zero ($B=0$), or the velocity is parallel or antiparallel to the magnetic field ($\theta = 90^{\circ}$ or $180^{\circ}$).

Negative Charge Force Direction

When a charge changes from positive to negative, the magnetic force reverses direction.

Right-Hand Rule vs. Left-Hand Rule

The right hand is used for positive charges; using the left hand for a positive charge results in the opposite (incorrect) direction.

Uniform Circular Motion

The path followed by a charged particle when it enters a uniform magnetic field perpendicular to the field.

Helical Path

The spiral path followed by a particle that has both parallel and perpendicular velocity components in a magnetic field.

Biot–Savart Law

A law describing the magnetic field produced by a small current element, where the field depends on current ($I$), length ($dl$), distance ($r$), and the angle ($\theta$).

Biot–Savart Formula

$$dB = \frac{\mu_0 I \, dl \sin(\theta)}{4\pi r^2}$$

Inverse Square Relationship in Magnetic Fields

The magnetic field from a current element decreases with the square of the distance ($1/r^2$); doubling the distance makes the field one-fourth as strong.

Right-Hand Rule for Wires

A method to determine field direction: point the thumb in the direction of current and curled fingers show the direction of the magnetic field.

Ampre’s Law

Relates the magnetic field around a closed loop to the current enclosed; most useful for symmetric situations like long straight wires, solenoids, and toroids.

Solenoid

A coil where the magnetic field inside is approximately uniform ($B = \mu_0 n I$) and the field outside is nearly zero due to cancellation.

Toroid

A solenoid bent into a circular ring where the magnetic field forms closed loops inside the core.

Toroid Magnetic Field Strength

The field is stronger at the inner radius and weaker at the outer radius, following the relationship $B \propto 1/r$.

Magnetic Flux (\Phi_B)

$\Phi_B = BA \cos(\theta)$, where variables include magnetic field strength ($B$), area ($A$), and angle ($\theta$).

Faraday’s Law

States that a faster change in magnetic flux or a higher number of turns ($N$) results in a larger induced emf.

Lenz’s Law

The principle that an induced emf always opposes the change in magnetic flux that produced it, represented by the negative sign in Faraday’s Law.

Alternating Emf (AC) in Rotating Loops

Produced as the angle between the magnetic field and the loop changes continuously, causing flux to change sinusoidally.

Inductance

A property of a coil or circuit that measures its ability to produce an induced emf to oppose changes in current.

Self-inductance

When a changing current in a coil induces an emf within that same coil.

Inductor Energy Formula

Energy stored in the magnetic field surrounding the inductor, calculated as $U = \frac{1}{2} L I^2$.

LC Circuit Energy Oscillation

The continuous transfer of energy between electric energy in the capacitor and magnetic energy in the inductor.

Kirchhoff’s Junction Rule

The total current entering a junction must equal the total current leaving the junction.

Parallel Circuit Voltage

The voltage across all resistors connected in parallel is the same.