Magnetic field lines are unaffected by nonmagnetic materials such as air, vacuum, paper, glass, wood, or plastics
magnetic fieldlines in a magnetic substance
is concentrated when a magnetic substance such as iron is placed in the field. Inside the iron, the field lines are more dense, compared with the field in air.
the end of the bar magnet is called
north seeking pole
opposite end of the bar magnet is called
south seeking pole
the earth's geographic north pole has
south magnetic polarity
the earth's geographic south pole has
north magnetic polarity
magnetic flux
The entire group of magnetic field lines, which can be considered flowing outward from the north pole of a magnet
magnetic flux
symbol (phi) ϕ
stronger the magnetic field has more lines of force and more flux
One maxwell (Mx) unit equals one magnetic field line
james clerk maxwell
proved that electromagnetic phenomena travel in waves at the speed of light.
the Weber
the larger unit of magnetic flux
one weber
1×108lines or maxwells
one microweber
100 lines or maxwells
flux density
the number of magnetic fi eld lines perunitarea of a section perpendicular to the direction of flux
flux density formula
B=Aϕ
CGS unit for flux density
The Gauss
The SI unit of flux density
The Tesla
comparison of flux and flux density
flux is total area, flux density is specified unit area
induction
The electric or magnetic effect of one body on another without any physical contact between them
a permanent magnet can induce an unmagnetized iron bar to become a magnet without the two touching. The iron bar then becomes a magnet
Note that the north pole of the permanent magnet 7 induces an opposite south pole at this end of the iron bar
permeability
This ability to concentrate magnetic flux
air gap
the air space between the poles of a magnet
The shorter the air gap, the stronger the field in the gap for a given pole strength. Since air is not magnetic and cannot concentrate magnetic lines, a larger air gap provides additional space for the magnetic lines to spread out
The purpose of a short air gap is to concentrate the magnetic fi eld outside the magnet for maximum induction in a magnetic material placed in the gap
The small part of the fi eld in the air is called leakage flux
A toroid is made in the form of a doughnut.
The principle of the closed magnetic ring is used to protect permanent magnets in storage
keeper for a magnet
The keeper maintains the strength of the permanent magnet as it becomes magnetized by induction to form a closed loop
an alternating fi eld can demagnetize the magnet.
The two broad classes are permanent magnets and electromagnets
electromagnet needs current from an external source to maintain its magnetic field.
permanent magnet, not only is its magnetic field present without any external current, but the magnet can also maintain its strength indefinitely
Sharp mechanical shock as well as extreme heat, however, can cause demagnetization
Current in a wire conductor has an associated magnetic field
With the length much greater than its width, the coil is called a solenoid.
More current and more turns make a stronger magnetic field
Soft iron is generally used for the core because it is easily magnetized and demagnetized.
A relay is a switch with contacts that are opened or closed by an electromagnet.