chapter 3 Flashcards
3 types of magnets
.natural lodestone
.permanent magnets magnets like these are are magnitised electrically by means of a solenoid.
.electromagnets when magnetic field passes through a coil a magnetic field similar to that of a bar magnet is established.
lines of force
the space in which magnetic forces act , is termed magnetic field
magnetic flux
entire quantity of magnetic lines surrounding a magnet , taken as a whole , is called a magnetic flux.
flux density
number of lines per unit area is termed flux density.
magnetic poles
all magnets have a north seeking pole and a south seeking pole. they are simply the dividing line between the magnet and air or other surrounding mediums.
one of the phenomenea of an electric current is its ability to produce
a magnetic field around the current carriying conductor.
magnetism associated with current carrying conductors can be intensified by
by forming the conductor into a coil.
magnetic fmagnetic field strength is of an eleectromagnet is is dependtant on
mmf and lenghth of solenoid
magnetic field strength of coil can be strengthened by
increase in current
placing an iron core inside solenoid.
standard transformer
used to step a voltage up or down with corresponding increase or decrease in voltage.
advantages of standard transformers
. eeasy construction
.efficiency at full load is high 97%
.they have no moving parts
.requires little maintainence.
core of a transformer is built out of
aalternate layers of lightly insulated alloyed steel laminations.
coils of transformers are made of
thinly insulated copper conductors
cooling of transformers
the diispation of heat losses generated in a transformer is of great nb since the rating of the transformer is determined not only by these losses but also by the temperature rise of the transformer.
open air cooling is applicable to
smaller transformers
oil cooling of a transformer
oil that the the core of the transformer is immersed in has a duel perpose , improves the insulation qualities and conduxts heat away from the windings and core to the cooling surfaces of the tank.
principle of operating a transformer
coils are electrically seperate by means op insulation
coils are magnetically coupled by means of a laminated iron core.
when a ac is applied to the primary winding:
. ac current flow through it.
.sets up an alternating flux around the iron core.
.which links to the secondary winding
.inducing in it an emf of the same frequancy.
define mutual inductance
if two coils are so arranged that the magnetic flux set up by the current in the primary coil links with the secondary coil , the two coils are said to have a mutual inductance. it is measured in henry
define the term the henry
two circuits have a mutual inductance of one henry if the emf induced in the secondary circuit is 1 volt when the current in primary circuit changes at the rate of 1 ampere per second.
ideal transformers
transformer assumed to havae no losses.
what is an auto transformer
primary and secondary windings are connected electrically and magnetically
uses for auto transformers
voltage regulation regulation on transmission lines , reduced voltage starting of three phase motors and high voltage starting of discharge lamps.
name one danger of an auto transformer
with a step up step down transsformer , there is a distinct danger of hte full primary voltage appeaaring across the terminals of the secondary winding in the event of an open circuit occuring in the seccondary winding
electromsgnetic induction
when a conductor moved through a magnetic field , an emf is induced in that conductor. if the conductor forms a closed circuit , an electricc current will flow. this is in accordance with faradays laws of electromagneetic induction
