vocabulary
electromagnetism
interaction of electric currents (or fields) and magnetic fields.
solenoid
coil of wire, usually cylindrical, that uses electric current to create a magnetic field.
armature
rotating part of an electric motor containing electromagnets.
electromagentic induction
inducing (or creating) a voltage in a conductor by changing the magnetic field near the conductor.
transformer
device that increases or decreases voltage in AC circuits in order to minimize energy lost during transmission.
permeability of free space
physical constant describing how effectively a magnetic field can be established in a vacuum. Also called the vacuum permeability. The permeability of free space is used in the equation for the magnetic field surrounding a current-carrying wire.
cathode ray tube (CRT)
vacuum tube in which a cathode emits a beam of electrons that are deflected by magnetic fields before hitting a phosphorescent screen. By suitably controlling the signal in the electromagnets, an image can be created on the screen.
electromagnets
magnets that are created by the flow of electricity.
electric motor
machine that transforms or converts electrical energy into mechanical energy.
magnetic flux
measure of the strength of a magnetic field through an area. Magnetic flux is measured in tesla square meters (T m2) or webers (Wb).
lenz law
direction of the current induced in a wire is such that the current’s induced magnetic field opposes the change in magnetic field that originally induced the current.
mass spectrometer
scientific instrument used to measure the masses of individual atoms in a gas using the force exerted on them in a uniform magnetic field. The instrument can be used to identify the elements and isotopes present in a gas.
voice coil
cylindrical coil of wire attached to the loudspeaker cone and moves in and out in response to a varying electrical signal passing through the wire. In a microphone, the equivalent device called an induction coil moves in response to sound waves, inducing a varying electrical signal in the wire.
polarity
condition of a system that describes opposing physical characteristics. Examples include the poles of a magnet and electrical charges.
commutator
device attached to the armature of a motor (or generator) that provides an electrical connection and allows the direction of current to be changed periodically during the rotation of the motor. In an electric motor, the commutator plates typically comes in electrical contact with the brushes.
faradays law of induction
changing magnetic flux through a coil of wire will induce an emf in the wire that is proportional to the number of loops and the rate of change of the magnetic field.
electrical generator
machine that converts rotational motion to electricity.
cycloton radius
radius of circular (or helical) motion of a charged particle moving in a uniform magnetic field. Also called gyroradius.
galvanometer
instrument used to detect very small electric currents by detecting the magnetic force on a loop of wire.
electric potential energy
change in potential energy per unit charge in an electric field.
electric field
force field created by electric charge. Electric field is a vector with the direction that a positive test charge would move, and whose magnitude is the force per unit charge. Measured in force per unit charge with units of newtons per coulomb, abbreviated N/C.
coulombs law
attraction or repulsion between two charged objects is inversely related to the square of the distance between them and directly related to the magnitude of each of the charges. Also expressed as Fe = keq1q2/r2.
electrically neutral
object that has a net charge of zero.
magnetic domains
region of a material comprised of many atoms with their individual magnetic fields aligned. By having their magnetic fields aligned they add together rather than cancel each other out.
force field
field that exerts a force on objects in it. Examples include magnetic, electric, and gravitational fields.