Unit 17 Inductance in AC Circuits

Question 1

Induced voltage is proportional

Answer 1

to the rate of change of current.

Question 2

Induced voltage is always opposite

Answer 2

in polarity to the applied voltage.

Question 3

Inductive reactance is a counter voltage that limits the

Answer 3

flow of current, as does resistance.

Question 4

Inductive reactance is measured in

Answer 4

ohms.

Question 5

Inductive reactance is symbolized by

Answer 5

XL .

Question 6

Inductance is measured in

Answer 6

henrys (H) and is symbolized by the letter L .

Question 7

When inductors are connected in series,the total inductance is equal to

Answer 7

the sum of all the inductors.

Question 8

The current lags the applied voltage by

Answer 8

90 Dgees in a pure inductive circuit.

Question 9

All inductors contain some

Answer 9

amount of resistance.

Question 10

The Q of an inductor is the ratio of the inductive

Answer 10

reactance to the resistance.

Question 11

Inductors with a Q of 10 are generally considered to be

Answer 11

“pure” inductors.

Question 12

Pure inductive circuits contain

Answer 12

no true power or watts.

Question 13

Reactive power is measured in

Answer 13

VARs.

Question 14

VARs is an abbreviation for

Answer 14

volt-amperes-reactive.

Question 15

How many degrees are the current and voltage out of phase with each other in a pure resistive circuit?

Answer 15

Zero Degrees

Question 16

3. To what is inductive reactance proportional?

Answer 16

to the inductance of the coil and the

frequency of the line.

Question 17

This current-limiting property of the inductor is called

Answer 17

reactance and is symbolized by the letter X .

This reactance is caused by inductance, so it is called inductive reactance and is symbolized by X L , pronounced “X sub L.”

Question 18

property of a circuit that tends to oppose

any change of current.

Answer 18

Inductance (L)

Question 19

The inductive reactance, in ohms, is caused by the induced voltage and is therefore proportional to the three factors that determine induced voltage:
What are they?

Answer 19

1. the number of turns of wire;
2. the strength of the magnetic field;
3. the speed of the cutting action (relative motion between the inductor and the magnetic lines of flux).

Question 20

The number of turns of wire and the strength of the magnetic field are determined by the physical construction of the inductor. Wat are they?

Answer 20

inductor. Factors such as the size of wire used, the number of turns, how close the turns are to each other, and the type of core material determine the amount of inductance (in henrys, H) of the coil

Question 21

The speed of the cutting action is proportional to the frequency (hertz).

Answer 21

An increase of frequency causes the magnetic lines of flux to cut the conductors at a faster rate and thus produces a higher induced voltage or more inductive reactance.

Question 22

current lag the what

Answer 22

Because the induced voltage is 180 Degrees out of phase with the applied voltage, the current lags the applied voltage by 90Degrees
pg 493

Question 23

Any power used

in an inductor is caused by losses such as the

Answer 23

resistance of the wire used to
construct the inductor, generally referred to as I²R losses, eddy current losses,
and hysteresis losses. pg 499

Question 24

volt-amperes-reactive (VARs) is used to measure the reactive power in a pure inductive circuit.

Answer 24

VARs = El x IL
or
VARs = EL² / XL
or
VARs = IL² x XL 

EL= voltage applied to an inductor
IL= current flow through an inductor 
XL= inductive reactance

Question 25

The amount of resistance compared with the inductive reactance determines 
the quality (Q) of the coil.

Answer 25

Q = XL / R

Question 26

inductors that have

a Q of 10 or greater are generally considered to be

Answer 26

pure inductors.

Question 27

Inductors constructed with many turns of small wire have a much higher resistance and therefore a higher or lower quality

Answer 27

a lower Q.

Question 28

Coil impedance is a combination of

Answer 28

wire resistance and inductive reactance.

Question 29

This total current-limiting effect is called impedance and is symbolized by the

Answer 29

letter Z.

Question 30

Coil impedance is a combination of

Answer 30

wire resistance and inductive reactance.

Question 31

Z =

Answer 31

resistance and inductive reactance.

Z= √R²+XL²

Question 32

To determine the inductance, it will be necessary to first determine the

Answer 32

amount of inductive reactance as compared to the wire resistance.

Question 33

The total current-limiting effect of the inductor is a combination of the inductive reactance and resistance. This total current-limiting effect is called impedance and is symbolized by the letter Z.

Answer 33

Z = E/R

Question 34

To determine the amount

of inductive reactance, use the following formula:

Answer 34

XL= √Z² - R²
Z = √R² + XL²
Z = E / I
L = XL / 2 πf

Question 35

The letter “Z” represent the Hypotenuse This total current-limiting effect is called ?

Answer 35

Z (impedance)