Glossary
Ampere-Maxwell Law
States that a magnetic field can be produced by both an electric current and a changing electric field (displacement current).
Example:
The Ampere-Maxwell Law explains how a magnetic field exists between the plates of a charging capacitor, even though no conduction current flows through the dielectric.
Electromagnetic Induction
The process by which a changing magnetic field induces an electromotive force (EMF) and thus an electric current in a conductor.
Example:
A generator uses electromagnetic induction to produce electricity by rotating coils of wire through a magnetic field.
Energy Stored in an Inductor
The energy stored in the magnetic field of an inductor when current flows through it, given by the formula U = (1/2)LI².
Example:
A large electromagnet stores significant energy stored in an inductor when a high current flows through its coils, which can be released as a powerful magnetic pulse.
Faraday's Law
States that the magnitude of the induced electromotive force (EMF) in a circuit is directly proportional to the rate of change of magnetic flux through the circuit.
Example:
If you quickly pull a magnet out of a coil of wire, Faraday's Law predicts a large induced voltage, which can light a small LED.
Gauss's Law for Electric Fields
States that the total electric flux through any closed surface is proportional to the total electric charge enclosed within that surface. It describes how electric fields originate from charges.
Example:
Using Gauss's Law for Electric Fields, you can calculate the electric field produced by a uniformly charged sphere without complex integration.
Gauss's Law for Magnetic Fields
States that the total magnetic flux through any closed surface is always zero, implying that magnetic monopoles do not exist and magnetic field lines always form closed loops.
Example:
Because of Gauss's Law for Magnetic Fields, you can never isolate a 'north' pole from a 'south' pole; if you break a magnet, you just get two smaller magnets.
Generators
Devices that convert mechanical energy into electrical energy by using electromagnetic induction.
Example:
Hydroelectric power plants use large generators to convert the kinetic energy of falling water into usable electricity for homes.
Inductance (L)
A property of an electrical conductor that opposes a change in the electric current flowing through it, by inducing an electromotive force (EMF) in the conductor itself. It's measured in henries (H).
Example:
A large inductance in a circuit means the current will take longer to reach its steady state after a voltage is applied, much like a heavy object takes more force to accelerate.
LR Circuit
An electrical circuit consisting of an inductor (L) and a resistor (R) connected in series or parallel.
Example:
When you turn on a motor, it behaves like an LR circuit, where the motor's coils act as an inductor, causing the current to build up gradually.
Lenz's Law
States that the direction of the induced current or EMF always opposes the change in magnetic flux that caused it, ensuring energy conservation.
Example:
When you drop a strong magnet through a copper pipe, Lenz's Law causes the magnet to fall slowly due to the opposing magnetic field created by the induced currents in the pipe.
Magnetic Flux (Φ_B)
A measure of the total number of magnetic field lines passing through a given area. It quantifies the amount of magnetic field 'flowing' through a surface.
Example:
The magnetic flux through a solar panel changes as the sun moves, which could be used to induce a current if the panel were part of a closed loop.
Maxwell's Equations
A set of four fundamental equations that describe how electric and magnetic fields are generated and altered by each other and by charges and currents.
Example:
The existence of light as an electromagnetic wave is a direct consequence of Maxwell's Equations, showing how changing electric and magnetic fields propagate through space.
Time Constant (τ)
In an LR circuit, the time constant is the time required for the current to reach approximately 63.2% of its maximum steady-state value. It is calculated as L/R.
Example:
If an LR circuit has a time constant of 0.1 seconds, the current will be nearly at its maximum value after about 0.5 seconds (5 time constants).
Transformers
Devices that change the voltage levels in AC circuits by using electromagnetic induction between two coils with different numbers of turns.
Example:
The small black box that charges your laptop is a transformer, stepping down the wall voltage to a lower, safer voltage for your device.