Iduction And Inductive Reactance

Question 1

Name 3 types of equipment where inductors are used.

Answer 1

1. Motors
2. Solenoid
3. Relay

Question 2

What is the symbol for inductance?

Answer 2

L

Question 3

What is the symbol for the unit of measurement of inductance?

Answer 3

H

Question 4

List the 4 factors that affect the inductance of a coil and the symbol for each.

Answer 4

N - number of turns of wire
u - Permeability
A - Cross sectional area
l - Length of cores magnetic path

Question 5

What is the formula for inductance (L)

Answer 5

L = N^2 u A / l

Question 6

What are 2 factors that affect the cemf of a coil?

Answer 6

Inductance of the coil

Rate of change of flux

Question 7

State Faradays Law

Answer 7

The amount of induced emf is directly proportional to the rate of change of flux

Question 8

What is mutual induction?

Answer 8

The generation of emf in a conductor or circuit by a change of flux around another conductor or circuit

Question 9

What is self induction?

Answer 9

The generation of an emf in a conductor or circuit by a change of flux in that conductor of circuit

Question 10

State Lenz’s Law

Answer 10

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

Question 11

Define time constant for an RL circuit

Answer 11

One time constant of an inductive circuit is the ratio of inductance (L) of the circuit divided by the resistance (R)

Question 12

During the time span of one time constant after closing an inductive circuit the current rises to ______ % of its steady value.

Answer 12

63.2%

Question 13

How many time constants are required for the current of a coil to reach a steady value?

Answer 13

5

Question 14

What is the equation for the time constant of a resistive-inductive circuit?

Answer 14

t = L / R

Question 15

What is the unit of measurement for a time constant?

Answer 15

Seconds

Question 16

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

Answer 16

b) decreases

Question 17

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

Answer 17

a) greater

Question 18

What happens when an inductive circuit is opened

Answer 18

The collapsing magnetic field can induce a high voltage into the circuit

Question 19

What is the purpose of a discharge resistor

Answer 19

Reduces arching at the switch when an inductive circuit is switched open

Question 20

Inductive reactance is the __________ created by inductance in an AC circuit.

Answer 20

Inductive reactance is the opposition created by inductance in an AC circuit.

Question 21

The symbol for inductive reactance is _____ and the unit of measurement is _____.

Answer 21

The symbol for inductive reactance is XL and the unit of measurement is ohm.

Question 22

What are the 2 factors affecting the inductive reactance

Answer 22

Inductance of the coil

Frequency of the supply voltage

Question 23

What is the equation for inductive reactance

Answer 23

XL = 2 Pi f L

Question 24

State the phase relationship between VXL and IXL in a purely inductive circuit.

Answer 24

IXL lags VXL by 90 degrees.

Question 25

What is the formula for reactive power?

Answer 25

Q = VX x IX

Reactive power = reactive voltage x reactive current

Question 26

What is reactive power?

Answer 26

The rate at which energy is being stored and then returned to a circuit.

Question 27

The symbol for reactive power is ____ measured in _____.

Answer 27

Q

var

Question 28

A simple inductor is made up of a __________ ________ and a ________.

Answer 28

A simple inductor is made up of a insulated wire and a core.