Induction and Inductive Reactance Flashcards
A simple inductor is made up of _____ _____ wound around a _____
insulated wire, core
name three types of equipment where inductors are used
motors, solenoids, relays or magnetic starter coils, electromagnetic lighting ballasts, VFD line reactors
what is the symbol for inductance?
L
what is the symbol for the unit of measurement for inductance?
H
list the four factors that affect the inductance of a coil and the symbol for each
number of turns, permeability, cross-sectional area of core, length of magnetic path
state Faraday’s Law
the amount of induced emf is directly proportional to the rate of change of flux
what is mutual induction?
generation of an emf in one conductor or circuit by a change of flux around another separate conductor or circuit
what is self-induction?
generation of an emf in a conductor or circuit by a change of flux in that conductor or circuit
state Lenz’s Law
the polarity of an induced voltage must be such that any current resulting from it develops a flux that tends to oppose any change in the original flux
what are the two factors that affect the cemf of a coil?
the inductance of the coil, the rate of change of current
define time constant for an RL circuit
L/R
During the time span of one time constant after closing an inductive circuit, the current risers to ____ % of its steady value
63.2%
how many time constants are required for the current of a coil to reach a steady value?
five
If the iron core of a coil is moved, the time taken for current to reach its steady value:
decreases
Describe what happens when an inductive circuit is opened
the collapsing magnetic field can induce a very high voltage into the circuit
what is the purpose of a discharge resistor?
reduces arcing at the switch when an inductive circuit is opened
Inductive reactance is the ______ created by inductance in an ac circuit
opposition
the symbol for inductive reactance is _____ and its unit of measurement is ____
XL, ohms
what are the two factors affecting the inductive reactance?
inductance of the coil, frequency of the supply voltage
state the phase relationship between Vxl and I(XL) in a purely inductive circuit
I(XL) lags V(XL) by 90 degrees
Define reactive power
the rate at which energy is stored and then returned to the circuit
the symbol for reactive power is ____
Q
