Glossary
Area Vector
A vector perpendicular to a surface, whose magnitude is equal to the area of the surface. It is used to determine the orientation of the surface relative to a magnetic field.
Example:
For a flat sheet of paper, the area vector would point straight out from the paper's surface.
Electromagnetic Induction
The process by which a changing magnetic field through a conductor induces an electromotive force (emf) and, consequently, an electric current.
Example:
When you wave a magnet near a coil of wire, you are demonstrating electromagnetic induction by generating a small current.
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:
A power plant's generator uses Faraday's Law to produce electricity by rotating coils through a magnetic field, constantly changing the magnetic flux.
Generators
Devices that convert mechanical energy into electrical energy by rotating a coil within a magnetic field, inducing an electromotive force and current.
Example:
Wind turbines use large generators to convert the kinetic energy of wind into usable electrical power.
Induced Current
The electric current generated in a conductor due to a changing magnetic flux, driven by the induced electromotive force.
Example:
When a car's alternator spins, it creates an induced current that recharges the car battery.
Induced Electromotive Force (emf)
The voltage generated across a conductor or circuit due to a changing magnetic flux, which can drive an induced current.
Example:
When a metal detector sweeps over a buried coin, the changing magnetic field induces an induced electromotive force in the coin, which the detector senses.
Induction Cooktops
Cooking appliances that heat cookware directly by inducing eddy currents within the metal through a rapidly changing magnetic field.
Example:
An induction cooktop heats a pot of water much faster than a traditional stove because it directly heats the pot itself, not the air around it.
Lenz's Law
States that the direction of the induced current (and emf) is always such that it opposes the change in magnetic flux that caused it.
Example:
If you drop a strong magnet through a copper pipe, it falls slower than expected because Lenz's Law creates an opposing magnetic field.
Magnetic Braking
A braking system that uses induced eddy currents in a moving conductor within a magnetic field to create a resistive force, slowing down the object without physical contact.
Example:
Some high-speed trains use magnetic braking to smoothly and efficiently slow down by generating opposing forces.
Magnetic Flux (Φ)
A measure of the total amount of magnetic field lines passing perpendicularly through a given area. It quantifies how much magnetic field 'pierces' a surface.
Example:
If a compass needle is placed inside a coil, the number of magnetic field lines passing through the coil's opening represents the magnetic flux.
Right-Hand Rule
A mnemonic used to determine the direction of magnetic fields, forces, or induced currents based on the orientation of the thumb and fingers of the right hand.
Example:
To find the direction of the magnetic field around a current-carrying wire, you can use the right-hand rule by pointing your thumb in the current's direction.
Transformers
Devices that change the voltage of alternating current by using electromagnetic induction between two coils with different numbers of turns.
Example:
The large boxes on power poles are transformers, stepping down high voltage electricity from power lines to a safer voltage for homes.