Chapter 19 - Inductance

Question 1

Define Inductance

Answer 1

Inductance, L — the ability of a conductor to produce an induced voltage in itself when the current changes.

Note : Inductance can also be defined as the characteristic that opposes any change in current.

Question 2

What is Leakage Flux?

Answer 2

Leakage flux is:

Any magnetic field lines that do not link two coils that are close to each other.

Question 3

Lenz’s law—

Answer 3

Lenz’s law states that the polarity of an induced voltage must be such that it opposes the current that produces the induced voltage.

Question 4

Henry (H) —

Answer 4

Is the basic unit of inductance.

Question 5

When current flow decreases

Answer 5

The magnetic field contracts

Question 6

When current flow increases

Answer 6

The magnetic field expands

Question 7

The Voltage induced is —

Answer 7

Opposite to the voltage applied

Question 8

If the current is constant,

Answer 8

No voltage is induced into the coil.

Question 9

Induced voltage decreases as

Answer 9

current increases

Question 10

Transformers do not

Answer 10

Change the AC Hz

Question 11

EP, ES, NP, NS definitions —

Answer 11

EP = Primary voltage
ES = Secondary voltage
NP= Number of primary turns
NS = Number of secondary turns

Question 12

If EP = 120, NP = 5, and NS = 1

then find ES

Answer 12

1st: Substitute - EP/ES = NP/NS

Cross multiply EP by NS, then that divide by NP to get ES.
120 x 1 = 120,
120 divided by 5 = 24,
ES = 24

Question 13

Current formulas:

Answer 13

I-T = E/XLT (current total)

Primary current: I-p = Pp/Ep, (Primary-power/Primary-voltage)

Secondary current: I-s = ES/RL (voltage divided by your RT)

Question 14

In series circuit

Answer 14

Total inductance (XL) is calculated like total resistance.

XL1 + XL2 + XL3 + etc..

Note: RT and XLT or (XL) cannot be added together.

Question 15

Definitions:
6.28 is pi (3.14) times 2 = 6.28
HZ = Frequency
H = Henry (H), (mH), etc..

Find the resistance of L1

Answer 15

To find the resistance of L1 in a circuit, 
we multiply (6.28 x Hz x H) = XL

Furthermore, multiply your XL by your current to find your voltage drop.

Question 16

Voltage

Answer 16

Leads current by 90 degrees.

Question 17

The combined opposition to current flow from the resistor and inductance, is called —

Answer 17

Impedance (Z)

Question 18

The formula for total impedance (ZT) is:

Answer 18

ZT = The square root of (RT squared + XL squared)

“Only for Series Circuits is the simple square root one applied”

Question 19

How much is the self-induced voltage across a 4-H inductance produced by a current change of 12A/s?

Answer 19

VL = L di
——
dt

= 4 x 12

= 48V

Question 20

The current through a 200-mH L changes from 0 to 100mA in 2micro-seconds.

How much is VL?

Answer 20

VL = L di/dt

                          100 x 10mA = 200 x 10mA x  ———————
                          2 x 10microA

= 10,000 or 10kV