Electromagnetic Induction and Magnetism & Matter Flashcards

Vocabulary practice flashcards covering fundamental definitions, equations, and material properties from Chapter 6 (Electromagnetic Induction) and Chapter 5 (Magnetism and Matter).

Electromagnetic Induction

The phenomenon in which electric current is generated in closed coils when subjected to varying magnetic fields.

Magnetic Flux ($\Phi_B$)

The scalar quantity representing the magnetic field passing through a plane of area $A$, defined as $\times$ dot product $\frac{}{}$ formula $\text{Wb}$ or $\text{T}\text{m}^2$: $\text{Magnetic Flux} = \rho \times ...$ or $\rho_B = \text{B} \times \text{A} = BA \rho \text{cos}(\theta)$, measured in weber ($\text{Wb}$) or tesla metre squared ($\text{T}\text{m}^2$).

Faraday's Law of Electromagnetic Induction

States that the magnitude of induced emf is equal to the time rate of change of magnetic flux through the circuit, expressed as \text{\theta} = -\frac{d\text{\rho}_B}{dt} or \text{\theta} = -N \frac{d\text{\rho}_B}{dt} for a coil of $N$ turns.

Lenz's Law

States that the induced current is in such a direction that it opposes the change in magnetic flux that produced it, which ensures conservation of energy.

Motional Electromotive Force

The emf produced between the ends of a conductor of length $l$ moving with speed $v$ in a uniform magnetic field $B$ perpendicular to both, given by \text{\theta} = Blv.

Inductance

The property of a coil where flux through it is proportional to current (\text{\rho} = LI), having SI unit henry ($\text{H}$) and dimensions $[\text{M}\text{L}^2 \text{T}^{-2}\text{A}^{-2}]$.

Self-Induction

The production of an induced emf in an isolated coil by varying current through the same coil, given by \text{\theta} = -L \frac{dI}{dt}.

Back EMF

The self-induced emf that opposes any change in current in a circuit, serving as the electromagnetic analogue of inertia in mechanics.

Energy Stored in an Inductor

The magnetic potential energy stored when establishing current $I$ in an inductor of self-inductance $L$, given by $W = \frac{1}{2} L I^2$.

Mutual Induction

The phenomenon of producing an induced emf in a coil by varying the current through a neighbouring coil, given by \text{\theta} = -M \frac{dI}{dt}.

Mutual Inductance of Two Co-axial Solenoids

The mutual inductance between two long co-axial solenoids of length $l$, given by M_{12} = M_{21} = \text{\rho}_0 n_1 n_2 A_1 l (or M = \text{\rho}_r \text{\rho}_0 n_1 n_2 A_1 l when filled with a medium of relative permeability \text{\rho}_r).

AC Generator Operation

Converts mechanical energy into electrical energy by mechanically rotating a coil of $N$ turns in a uniform magnetic field, inducing an alternating emf \text{\theta} = \text{\theta}_0 \text{sin}(\text{\rho} t) where \text{\theta}_0 = NBA\text{\rho}.

Magnetic Field Lines Comparison

Continuous closed loops formed around magnetic elements that run from N to S pole outside and S to N pole inside, where the tangent at any point gives the direction of magnetic field $\text{B}$.

Gauss's Law for Magnetism

States that the net magnetic flux through any closed surface is zero (\text{\rho} = \text{\rho} \text{B} \times d\text{s} = 0), implying there are no magnetic monopoles.

Magnetisation ($M$)

The average magnetic dipole moment per unit volume ($M = \frac{m_{\text{net}}}{V}$), having unit $\text{A}\text{m}^{-1}$ and dimension $[\text{A}\text{L}^{-1}]$.

Magnetic Intensity ($H$)

A quantity defined as H = \frac{B}{\text{\rho}_0} - M, which simplifies to H = \frac{B}{\text{\rho}_0} in a vacuum.

Magnetic Susceptibility (\text{\rho}_m)

A measure of the degree of magnetisation produced by a unit field, defined as \text{\rho}_m = \frac{M}{H}.

Diamagnetism

The property of substances with small negative magnetic susceptibility (\text{\rho}_m < 0) and relative permeability \text{\rho}_r < 1 that are weakly repelled by an external magnetic field (e.g., Bi, Cu, Hg, Ag, water, NaCl).

Paramagnetism

The property of substances with small positive magnetic susceptibility (0 < \text{\rho}_m < 1) and relative permeability \text{\rho}_r > 1 that are weakly attracted by an external magnetic field (e.g., Al, Pt, $\text{O}_2$, Mg, Na).

Ferromagnetism

The property of substances with large positive magnetic susceptibility (\text{\rho}_m \text{\rho}\text{\rho} 1) and relative permeability \text{\rho}_r \text{\rho}\text{\rho} 1 that are strongly attracted by an external magnetic field (e.g., Fe, Co, Ni, Gd, $\text{Fe}_2\text{O}_3$).

Hard Magnetic Materials

Ferromagnetic materials characterized by high retentivity and high coercivity, used for permanent magnets (e.g., Alnico, steel, hard ferrites).

Soft Magnetic Materials

Ferromagnetic materials characterized by low retentivity and low coercivity that are easily magnetised and demagnetised, used for transformer cores and relays (e.g., soft iron, silicon steel).