Electromagnetic Induction Vocabulary Flashcards

Vocabulary terms and definitions based on lecture notes covering electromagnetic induction, self/mutual induction, and transformers.

Magnetic flux

The total number of magnetic field lines crossing a surface normally, represented as $\phi = \oint \mathbf{B} \cdot d\mathbf{s} = B A \cos(\theta)$.

Magnetic flux density

Also termed as magnetic field ($B$), it is defined as the total number of magnetic field lines crossing per unit area normally ($B = \frac{\phi}{A}$).

Weber

The SI unit of magnetic flux, where $1\,\text{Wb} = 1\,\text{T} \times \text{m}^2$.

Maxwell

The C.g.s unit of magnetic flux, where $1\,\text{Wb} = 10^8\,\text{maxwell}$.

Principle of electromagnetic induction

The phenomenon where a change of magnetic flux associated with a coil or conductor produces an induced emf and hence an induced current in the coil.

Faraday's Law

A law stating that whenever the magnetic flux associated with a closed circuit changes, an induced emf and hence an induced current is produced in the circuit, lasting as long as the change in flux takes place ($e = -\frac{d\phi}{dt}$).

Lenz's Law

A law stating that the direction of induced current is such that it opposes the cause which produced it.

Self Induction

The phenomenon of production of induced emf in a coil when the current in the coil changes.

Coefficient of self-induction

Also called self-inductance ($L$), it is defined as the induced emf set up in a coil when the rate of change of current is unity ($1\,\text{A/s}$).

Henry

The unit of self-inductance and mutual inductance; $1\,\text{henry}$ is set up when an emf of $1\,\text{volt}$ is produced by a rate of change of current of $1\,\text{ampere per second}$.

Motional emf

The induced emf produced by changing the area of a coil moving in a magnetic field, given by $e = B l v$.

Induced charge

The charge $dq = \frac{d\phi}{R}$ produced during induction, which depends on the net change in magnetic flux and does not depend on the rate of change of magnetic flux.

Peak emf

The maximum induced emf set up when a coil with $N$ turns rotates in a uniform magnetic field, given by $e_0 = N B A \omega$.

Self-inductance of a long solenoid

The self-inductance of a long solenoid given by $L = \frac{\mu_0 N^2 A}{l}$ or $L = \frac{\mu_r \mu_0 N^2 A}{l}$ when wound over a material of permeability $\mu_r$.

Mutual Induction

The phenomenon of production of induced emf in one coil due to a change of current in the neighboring coil.

Mutual inductance of two long solenoids

The mutual inductance between two solenoids given by $M_{12} = M_{21} = \frac{\mu_0 \mu_r N_1 N_2 A}{l}$, where $A$ is the common area of cross section.

Transformer

A device operating on the principle of mutual induction used for converting an alternating current at low voltage into that at high voltage and vice versa.

Step up transformer

A transformer where the output voltage is increased, characterized by $N_s > N_p$ and $e_s > e_p$.

Step down transformer

A transformer where the output voltage is decreased, characterized by $N_p > N_s$ and $e_p > e_s$.

Copper loss

Power loss ($I^2 R$) occurring due to heating of primary and secondary coils in a transformer, minimized by using thick copper wires.

Eddy current loss

Heat energy loss in the iron core of a transformer caused by alternating magnetic flux inducing eddy currents, minimized by using a laminated iron core.

Flux leakage

Energy loss occurring when the magnetic flux in the primary coil is not completely linked with the secondary coil, minimized by winding primary and secondary coils one over another.

Hysteresis loss

Energy lost as heat due to repeated magnetisation and demagnetisation of the iron core, minimized by using a core material with a narrow hysteresis loop.