Moving Charges and Magnetism

Flashcards covering key vocabulary, formulas, and concepts from the Moving Charges and Magnetism physics lecture.

Magnetic Field

A physical reality produced by moving charges that can exert force on other moving charges, measured in Tesla ($T$).

Tesla ($T$)

The SI unit of magnetic field, equivalent to $1\,Ns/Cm$.

Gauss ($G$)

A unit of magnetic field strength where $1\,G = 10^{-4}\,T$. The magnetic field of Earth is approximately $3.6 \times 10^{-5}\,T$, or $0.36\,G$.

Lorentz Force

The total force experienced by a charged particle moving in a region where both electric and magnetic fields are present, expressed as $\mathbf{F} = q[\mathbf{E} + (\mathbf{v} \times \mathbf{B})]$.

Fleming's Left Hand Rule

A rule used to determine the direction of magnetic force: the thumb indicates force, the forefinger indicates magnetic field ($B$), and the middle finger indicates current (direction of positive charge).

Pitch

The distance moved in one rotation by a charged particle following a helical path when its velocity is at an arbitrary angle to the magnetic field, calculated as $p = v\cos(\theta) \times T$.

Velocity Selector

A device where mutually perpendicular electric and magnetic fields are used to separate charges with a specific velocity; particles with $v = \frac{E}{B}$ pass through without deflection.

Cyclotron

A device used to accelerate charged particles like protons, deuterons, and alpha particles to very high velocities using alternating voltage and a strong magnetic field.

Ampere's Circuital Law

A law stating that the closed line integral of the magnetic field around any circuit is equal to $\mu_0$ times the total current $I$ passing through it: $\oint \mathbf{B} \cdot d\mathbf{l} = \mu_0 I$.

Solenoid

A long coil of wire where the magnetic field inside is uniform and expressed as $B = \mu_0 nI$, while the field outside is negligible.

Toroid

A hollow circular ring on which a large number of turns of a wire are closely wound, creating a magnetic field inside the core.

Definition of 1 Ampere ($A$)

The current which, when passed through two parallel conductors placed $1\,m$ apart, produces a force per unit length of $2 \times 10^{-7}\,N/m$.

Biot-Savart Law

A law that calculates the magnetic field ($dB$) produced by a current element ($dl$), stated as $dB = \frac{\mu_0}{4\pi} \frac{I\,dl\sin(\theta)}{r^2}$.

Magnetic Moment ($m$)

The product of the current and the area of a loop ($m = IA$ or $m = NIA$ for $N$ turns), with the SI unit $Am^2$.

Current Sensitivity

The deflection per unit current in a galvanometer, represented as $\frac{\phi}{I} = \frac{NAB}{k}$.

Voltage Sensitivity

The deflection per unit voltage in a galvanometer, calculated as $\frac{\phi}{V} = \frac{NAB}{kR}$.

Shunt Resistance

A small resistance connected in parallel to a galvanometer to convert it into an ammeter.

Aurora Borealis

A display of green and pink lights in polar regions caused by electrons and protons from solar flares getting trapped in Earth's magnetic field and colliding with atmospheric atoms.

Gyromagnetic Ratio

The ratio of the magnetic moment to the angular momentum of a particle; for an electron, it is $8.8 \times 10^{10}\,C/kg$.

Bohr Magneton

The magnetic moment due to the orbital motion of an electron in the first orbit of a hydrogen atom, equal to $9.27 \times 10^{-24}\,Am^2$.