Magnitism Powerpoint notes Flashcards
Several factors affect the strength of an electromagnetic coil.
These are:
* the ___ between coils for an air-core electromagnet
* the number of ___ in the coil
* the ___ of the current flowing through the coil
* the type of ___ from which the core is made.
* If the loops of the coil are wound closer together, more of the
flux lines are forced into the centre of the coil, increasing the
flux density and strengthening the field.
As the flux density is decreased, so is the strength.
As more loops are added to the coil, the fields combine to make the flux lines
through the coil more dense, increasing the strength of the magnetic field
spacing, turns, magnitude, material
____ (also referred to as magnetizing intensity or magnetizing gradient) is the measure of the magnetomotive
force(mmf) per unit length in a magnetic circuit
Magnetizing force
____ is the measure of the ease with which flux may be set up in a unit length and cross section of a material
Permeability
Whenever this induced voltage is produced
By cutting through flux lines - Either by the
conductor or moving the magnetic field this
Is called ____
Electromagnetic Induction
The ___ of voltage induced in a turn of wire
is directly proportional to the rate of change of flux
passing through the turn of wire
Faraday’s law
𝐸=𝛽 𝐿∨
E = generated voltage
= flux density in teslas
= the active length of the conductor in meters
= Speed with which the flux lines are cut
magnitude
The generated ___ can be controlled by:
* Increasing/decreasing the ___ (via current with a rheostat)
* Increasing/decreasing the active ___ of the conductor
* Increasing/decreasing the ___ of the rotating conductor (via the prime mover)
1volt = 1Wb/1sec
1 volt is generated when 1 weber is cut in 1 second
Voltage, flux density, length, speed
___ literally means circulating currents
They are loops of electric current induced within conductors by a changing magnetic field in the
conductor according to Faraday’s law of induction.
Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field.
Eddy currents
Eddy Currents
The ___ of the current in a given loop is proportional to the strength of the magnetic
field, the area of the loop, and the rate of change of flux, and inversely proportional to
the resistivity of the material.
These circular currents within a piece of metal look vaguely like eddies or whirlpools in a
liquid.
magnitude
Lenz’s Law
- If a magnet is moved toward a ___, magnetic lines of flux begin to cut the conductors of the coil and a current is
then induced in the coil. - This induced current causes magnetic lines of flux to expand outward around the coil.
- As this expanding magnetic field cuts through the conductors of the coil, a voltage is induced in the coil.
coil
Lenz’s
- When a ___ is induced, in a coil and there is a complete circuit, so current flows through the coil
- When current flows through the coil, a magnetic field is created around the coil.
- This magnetic field develops a polarity ___ that of the moving magnet.
- The magnetic field developed by the induced current acts to attract the moving magnet and pull it back inside
the coil.
voltage, opposite
Calculates ___
R-L Time Constants
T = L / R
T = time in seconds
L = inductance in henrys
R = resistance in ohms
Inductance
The Main difference between an AC Generator and a
DC generator is the Commutator
Commutator serves 2 purposes:
1. Converts ___ Voltage generated in the rotating
loop(the armature) to a __ voltage
2. Connects the brushes to the rotating loop giving
the voltage a “highway” out to the loads
AC, DC
Magnetomotive force
formula ___
Unit ___
I x N or I (Flux Density) x Rm (Reluctance)
Unit (A.t.)
ampere-turn
Flux
formula ___
Unit ___
Fm (Magnetomotive Force / Rm (Reluctance)
Unit (I)
Weber
