Moving Charges and Magnetism – Vocabulary Flashcards

Vocabulary flashcards covering key terms, definitions, and formulas from the lecture notes on moving charges and magnetism.

Hans Christian Oersted

Danish physicist (1777–1851) who first observed that an electric current deflects a magnetic compass needle, revealing the link between electricity and magnetism.

James Clerk Maxwell

Physicist who unified electricity, magnetism, and light in 1864, showing that light is an electromagnetic wave.

Magnetic Field (B)

A vector field produced by moving charges or currents that exerts forces on other moving charges; measured in tesla (T).

Lorentz Force

Total force on a charge q moving with velocity v in electric field E and magnetic field B: F = q(E + v × B).

Tesla (T)

SI unit of magnetic field; 1 T = 1 N·s / (C·m).

Gauss

Non-SI unit of magnetic field; 1 G = 10⁻⁴ T.

Right-Hand Rule (straight wire)

Grasp the wire with right hand so thumb points with current; curled fingers give direction of magnetic field circles.

Right-Hand Thumb Rule (loop)

Curl fingers in direction of current around a loop; out-stretched thumb gives direction of loop’s area vector and magnetic moment.

Magnetic Force on Conductor

Force on length l of wire carrying current I in field B: F = I l × B.

Cyclotron Frequency

Angular frequency of a charge q in uniform B: ω = qB/m; independent of speed and orbit radius.

Biot–Savart Law

Elemental field due to current element I dl: dB = (μ₀/4π)(I dl × r̂)/r².

Permeability of Free Space (μ₀)

Physical constant 4π × 10⁻⁷ T·m/A describing magnetic response of vacuum.

Ampere’s Circuital Law

Line integral of B around closed path equals μ₀ times total current enclosed: ∮B·dl = μ₀Iₑ.

Solenoid

Long, tightly wound helical coil; internal field is uniform: B = μ₀nI (n = turns per unit length).

Magnetic Dipole Moment (m)

Vector quantity for current loop: m = I A (area vector by right-hand rule).

Torque on Current Loop

In uniform B, loop experiences τ = m × B; magnitude τ = mB sin θ.

Moving-Coil Galvanometer

Sensitive instrument where a current-carrying coil in radial magnetic field deflects; used to detect small currents.

Shunt Resistance (rₛ)

Low resistance placed parallel to a galvanometer to convert it into an ammeter by bypassing most current.

Ammeter

Device for measuring current; realised by galvanometer with small shunt so overall resistance is low.

Voltmeter

Device for measuring potential difference; made by placing large series resistance with a galvanometer.

Current Sensitivity

Deflection per unit current of a galvanometer: (NAB)/k.

Voltage Sensitivity

Deflection per unit voltage of a voltmeter: (NAB)/(kR).

Principle of Superposition (B-field)

Total magnetic field at a point equals vector sum of fields produced by all sources.

Magnetic Field Lines

Closed loops indicating direction of B; unlike electric lines, they never begin or end.

Ampere (A)

Base SI unit of current; defined via force of 2 × 10⁻⁷ N m⁻¹ between two 1 m apart parallel conductors carrying equal currents.

Parallel Currents Attract

Two wires with currents in same direction experience mutual attraction; opposite directions repel.

Pitch of Helical Path

Distance moved along B in one complete rotation of a charged particle: p = v∥ T = 2πmv∥/(qB).

Oersted Experiment

Demonstrated compass deflection by current, showing currents produce magnetic fields.

Right-Hand Screw Rule

Direction of vector product A × B given by rotation from A to B; advance of right-hand screw gives resultant.

Drift Velocity (v_d)

Average velocity of charge carriers producing current in a conductor.

Current Density (j)

Current per unit area vector; related to drift velocity by j = nq v_d.

μ₀ε₀ Relation

Product μ₀ε₀ equals 1/c², linking electric and magnetic constants to light speed.

Tesla–Gauss Conversion

1 tesla equals 10,000 gauss (10⁴ G).

Field of Straight Wire

Magnitude B = μ₀I/(2πr) at distance r from an infinitely long wire.

Field at Loop Centre

Magnetic field at centre of circular loop: B = μ₀I/(2R).

Field Inside Long Solenoid

Uniform internal magnetic field: B = μ₀nI.

Magnetic Moment of N-Turn Loop

For N turns: m = NI A.

Cyclotron

Device using perpendicular electric and magnetic fields and constant cyclotron frequency to accelerate charged particles.

Biot–Savart vs Ampere

Both relate B to current; Ampere’s law is integral form useful with symmetry, derivable from Biot–Savart.

Lorentz Force Zero Condition

Magnetic component q v × B vanishes when velocity is parallel or antiparallel to magnetic field.