Iduction And Inductive Reactance Flashcards
(28 cards)
Name 3 types of equipment where inductors are used.
- Motors
- Solenoid
- Relay
What is the symbol for inductance?
L
What is the symbol for the unit of measurement of inductance?
H
List the 4 factors that affect the inductance of a coil and the symbol for each.
N - number of turns of wire
u - Permeability
A - Cross sectional area
l - Length of cores magnetic path
What is the formula for inductance (L)
L = N^2 u A / l
What are 2 factors that affect the cemf of a coil?
Inductance of the coil
Rate of change of flux
State Faradays Law
The amount of induced emf is directly proportional to the rate of change of flux
What is mutual induction?
The generation of emf in a conductor or circuit by a change of flux around another conductor or circuit
What is self induction?
The generation of an emf in a conductor or circuit by a change of flux in that conductor of circuit
State Lenz’s Law
The polarity of any induced voltage must be such that any current resulting from it develops a flux that tends to oppose any change in the original flux
Define time constant for an RL circuit
One time constant of an inductive circuit is the ratio of inductance (L) of the circuit divided by the resistance (R)
During the time span of one time constant after closing an inductive circuit the current rises to ______ % of its steady value.
63.2%
How many time constants are required for the current of a coil to reach a steady value?
5
What is the equation for the time constant of a resistive-inductive circuit?
t = L / R
What is the unit of measurement for a time constant?
Seconds
If the iron core of a coil is removed the time taken for the current to reach its steady value
a) increases
b) decreases
c) stays the same
b) decreases
If a circuit with 1000 turns of 30 AWG is replaced with 20 AWG wire, the time constant compared to the first coil would be
a) greater
b) less
c) the same
a) greater
What happens when an inductive circuit is opened
The collapsing magnetic field can induce a high voltage into the circuit
What is the purpose of a discharge resistor
Reduces arching at the switch when an inductive circuit is switched open
Inductive reactance is the __________ created by inductance in an AC circuit.
Inductive reactance is the opposition created by inductance in an AC circuit.
The symbol for inductive reactance is _____ and the unit of measurement is _____.
The symbol for inductive reactance is XL and the unit of measurement is ohm.
What are the 2 factors affecting the inductive reactance
Inductance of the coil
Frequency of the supply voltage
What is the equation for inductive reactance
XL = 2 Pi f L
State the phase relationship between VXL and IXL in a purely inductive circuit.
IXL lags VXL by 90 degrees.
