Theory

Question 1

Factors on EMF generation/ Faraday’s Law

Answer 1

-density of magnetic flux
-length of conductor within magnetic field
-rate at which conductor cuts lines of magnetic force

Question 2

Maximum cutting rate

Answer 2

90 degrees

Question 3

Components of AC sine wave

Answer 3

-One positive alternation (0 to 180)
-One negative alternation (180 to 360)

Question 4

Frequency

Answer 4

-number of electrical cycles per second
-symbol (f)
-unit of measurement (hertz)
-symbol of hertz (hz)
-time to complete one cycle (time period)

Question 5

Frequency formula

Answer 5

f= (p x n)/120

f=(pp x r/min)/60

Question 6

Maximum values at sine waves

Answer 6

+V at 90 degrees
-V at 270 degrees

Question 7

Instantaneous values of a cycle

Answer 7

e=Emax x sine of angle

Question 8

Effective Value/RMS value

Answer 8

Emax = E RMS / 0.707

Question 9

Impedance on AC circuit

Answer 9

Resistance
Inductive Reactance
Capacitive Reactance

Question 10

Inductance

Answer 10

Property of a circuit that opposes change of current
through a counter EMF
(L)
unit of measurement: Henry

Question 11

Inductive reactance

Answer 11

• Current limiting property of an inductor of a circuit
  (XL)
• measured in Ohms

XL = 2 pi f L

Question 12

Factors on AC resistance

Answer 12

• DC ohmic value
• Iron losses
• Dielectric losses
• Skin Effect

Question 13

Iron Losses

Answer 13

• Hysteresis loss and Eddy current loss

Question 14

Hysteresis loss

Answer 14

• energy it takes to overcome molecular friction due to reversing polarity
• use an alloy that contains Silicon for the core and armature

Question 15

Eddy Current loss

Answer 15

• circulating current induced in magnetic material that is adjacent to an AC circuit
• use laminations in the core and armature, less induced voltage

Question 16

Dielectric loss

Answer 16

• energy loss to circuit due to voltage stress of a conductor
• greater at high voltage

Question 17

Skin Effect

Answer 17

• tendency of AC to flow towards conductors surface
• effective area of conductor is reduced, resistance increases
• problem at high frequency
• allows transmission lines to have a steel core

Question 18

Inductor

Answer 18

• an insulated wire wrapped around a core
• coil, solenoid, reactor

Question 19

Factors that affect Inductance

Answer 19

L= (N^2 u A)/l

N(number of turns of a conductor)
u(permeability of core material)
A(cross-sectional area)
l(length of core’s magnetic path)

Question 20

Mutual Induction

Answer 20

• emf generated in one conductor by a change of flux around a separate circuit

Question 21

Lenz’s Law

Answer 21

• induced voltage attempts to force electron in one direction

Question 21

Self Induction

Answer 21

• emf generated by a change of flux around a conductor

Question 22

Left Hand Rule

Answer 22

• thumb points towards core
• forefinger points to direction of magnetic field
• middle finger points of of page, cemf

Question 23

Factors that affect CEMF

Answer 23

• inductance of coil
• rate of change of current

cemf= (change in current / change in time) x inductance

Question 24

Time Constants of inductive circuits

Answer 24

T= L/R - takes 5 time constants to reach steady value - one time constant = 63.2%

Question 25

Discharge Resistor

Answer 25

- placed in parallel to coil - reduces inductive kick - reduces arcing

Question 26

Inductive Circuits

Answer 26

Current lags voltage by 90 degrees

Question 27

Reactive Power/ Quadrature Power

Answer 27

Qxl = Vx x Ix Qxl = I^2 XL

Question 28

Capacitor Construction

Answer 28

2 plates of conducting material seperated by a insulating material called dielectric

Question 29

Non polarized Capacitors

Answer 29

Air Oil filled paper, tubular plastic film mica ceramic disc

Question 30

Capacitor applications

Answer 30

Timer Rectifier smoothing and filtering Power factor correction Motor starting

Question 31

Capacitance

Answer 31

capacitor ability to store charge measured in micro farads

Question 32

Factors that affect Capacitance

Answer 32

Area of plate distance between plates type of dielectric material

Question 33

Dielectric Constant

Answer 33

Rating of dielectric insulating material's ability to polarize and store charge compared to air

Question 34

Dielectric Strength

Answer 34

Ability to withstand volatge kV/mm

Question 35

Electric Charge

Answer 35

Q= I x t C= Q / V

Question 36

Time Constants in Capacitive circuits

Answer 36

T= R x C

Question 37

Capacitive reactance

Answer 37

Xc = 1/( 2 pi f C)

Question 38

Capacative phasor relationship

Answer 38

current leads voltage by 90 degrees

Question 39

Series AC Circuits

Answer 39

Total Resistance Rt =R1 + R2 +R3 ... Total Inductance Reactance XLt = XL1 + XL2 + XL3 ... Total Capacitive Reactance XCt = XC1 + XC2 + XC3 ..