Induction And Inductive Reactance
equation for cemf
e induced=rate ofnchange of current multiplied by inductance or cemf= (change of current/change of time)x inductance
greek symbol for permeability
greek letter mu
unit of measurement for inductance
henry
if inductance is high, cemf will be
high
time constant equations
r= L/R
there is a direct/indirect relationship between inductance of the circuit and the time required for one time constant
direct
the core can be altered in three ways:
- by using magnetic material with a differey permeability -by changin the cross-sectional area of the core -by changing core length
what are the two electrical properties of a coil?
- resistance - inductance
what are three factors that have an effect on the rate of change of flux
- rotational frequency- - flux density - angle of cutting (max is wy 90∘
inductance will increase when :
-the number of turns on the coil is increased - material with higher permeabilitz is used for the core - a core with larger cross sectional area is used - the length of the magnetic path is decreased
how many time constants are required for a current of a coil to reach a steady value
5
define mutal induction
Can be define as the generation of an emf in one conductor or circuit by a change of flux around a seperate conductor or ciruit
symbol for unit of measurement for inductance
H
higher core permeability=
Higher inductance
symbol for inductance
L
what is the equation for the factos affecting inductance?
L=(N²(mu)A )/ l ((number of turns ²) x mu x area) / length of magnetic path
what is the calculation for resistance?
R= (pxl)/A
if the iron core of a coil is removed, the time taken for the current to reach its steady calue will
decrease
equation for inductive reactance
XL=2πfL where: XL= inductive reactance π= 3.14 f= freqency in hertz L= inductance in henrys
define discharge resistor
a resistor to be conmected across the coil, either permamently or automatically- at the instant the switch opens
what is induction?
a voltage can be produced by moving a conductor through a magnetic field, or by moving a magneic field past a conductor . the process by which a voltage is produced by the interaction of magnetic fields and a conductor is known as induction.
what is the inducatance of a coil affected by?
coil- number of turns (N) core - Permabiliyy (mu) - Area (A) - Length of magnetic path (l)
what is a inductive kick
high voltage doesntnlast long but can cause some serious arcing at the switch unless the switch was designed to handle it, or a method is used to reduce the high voltage
larger core area =
higher inductance
more turns =
higher inductance
shorter path
higher inductance
the two factors affecting the inductive reactance are
inductance frequency
the counter emf induced in a coil depends on two factors
inductance of the coil the rate of change od current ( which determines the rate of change of flux)
difference betwee induction and inductance
inductance- the property of a circuit that opposes change in current induction- the provess by which voltage is produced by the interaction of a conductor and a magnetic field
in a real coil ( inductive and resistive)there is a _____ relationship between the resistance of the circuit and the required for one time constant
inverse if the resistance is high the steady current will be low, therefore the steady current value will be reached in a shorter period of time
what is the effect of an induced voltage?
it is that it will oppose the hange that produced it. since the induced voltage opposed any change, it is called a counter emf, cemf
define inductive reactance
it is the opposition created by inductance in an ac circuit
longer path
lower inductance
what are the two two distinct processes involving stationary conductors and moving field:
mutual induction self induction
what is the unit of measurement of inductive reactance
ohm
what is a henry
one ampere per second = 1 volt of counter emf induced = said to have inductance of one henry
what is the unit of measurement for a time constant?
second
define permeability
the ability of a magnetic materia lnto increase the strength of a magnet when inserted in the core
faradays law
the amount of emf induced in a conductor by the process of induction depends on the rate of change of flux
faradays law
the amount of induced emf is directly proportional to the rate of change of flux
define self induction
the generation of an emf in a conductor or circuit by a change of flux in the same circuit
flux density
the number of lines of force per unit area, such as the number of lines per cm² this is a measure of the strength of the magnetic field at the given spot
lenz's law
the polarity of any induced voltage mist be such that any curremt resulting from it will develop a flux that tends to oppose any change in the original flux
define inductance
the property of a circuit that opposes a change in current
what is rotational frequency?
the speed at which the coils rotate And cut the lines of force
time constant equation
the value of the time constant ( in seconds) is equal to the inductance ( in henrys) devided by the resistance ( in ohms)
