Magnetism: Fields and Currents (Video Notes)

Vocabulary flashcards covering key concepts from the video notes on magnetism, current loops, solenoids, and charged particle motion.

Magnetic field

A vector field describing the magnetic influence of magnets and currents; measured in tesla (T).

Tesla (T)

The SI unit of magnetic field strength; 1 T = 1 N/(A·m).

Permeability of free space (μ0)

A fundamental constant relating magnetic fields and currents in vacuum; μ0 ≈ 4π×10^-7 T·m/A.

Long straight wire magnetic field

The magnetic field around a long straight current-carrying wire is circular, with magnitude B = μ0 I /(2π r) and direction given by the right-hand rule.

Right-hand rule

A mnemonic to determine magnetic field direction around current-carrying conductors: point thumb along current, curl fingers to obtain the field direction.

Current loop

A closed loop of wire carrying current; produces a magnetic field with a defined axis and a north pole orientation determined by current direction.

Magnetic field at the center of a loop

For a circular loop of radius R with N turns carrying current I, the center field is B_center = μ0 N I /(2R); directed along the loop axis per the right-hand rule.

North pole of a current loop

The end where magnetic field lines emerge; its location is determined by the loop's current direction via the right-hand rule.

Solenoid

A long coil of wire; generates a relatively uniform magnetic field inside when current flows.

Turns per unit length (n)

The number of turns per unit length in a solenoid; the axial field scales as B ≈ μ0 n I (in the ideal case).

Magnetic field inside a solenoid

The nearly uniform axial field inside a long solenoid, approximately B ≈ μ0 n I.

Cyclotron motion

Circular motion of a charged particle moving perpendicular to a uniform B field; radius r = mv/(qB).

Helical path

A charged particle path with velocity components parallel and perpendicular to B, resulting in a spiral along the field lines.

Auroras

Light displays in Earth's atmosphere caused by charged particles spiraling along Earth's magnetic field lines and colliding with atmospheric gases.

Lorentz force

Magnetic force on a moving charge: F = q v × B; magnitude F = q v B sin θ; direction perpendicular to the plane formed by v and B.

Angle between velocity and magnetic field

θ; determines the component of velocity perpendicular to B; the magnetic force is maximal at θ = 90°.

Force on positive vs negative charges

Positive charges experience F = q v × B; negative charges experience the opposite direction.

Radius of circular motion in a field

For a charged particle in a perpendicular B field, r = mv/(qB) (cyclotron radius).

Superposition of magnetic fields

The net magnetic field is the vector sum of fields from multiple sources; fields from N loops add at the center.

Strong magnetic fields in nature

Earth’s strongest laboratory pulse ~1200 T (brief); neutron stars can host fields in the range ~10^4 to 10^11 T.