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Electrical Year 2 > D1 > Flashcards

D1 Flashcards

1
Q

What is Faradays law of electromagnetic induction?

A

The magnitude of the voltage induced in a turn of wire is proportional to the rate of change of flux passing through (or linked with) that turn.

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2
Q

What is Faradays law in a formula?

A

e=Blv
e = voltage generated in volts
B = flux density of the field in tesla
l = active length of the conductor in the field in metres
v = relative velocity of the conductor at right angles to the magnetic field in metres per second.

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3
Q

What is the active length of the conductor?

A

The portion of the conductor that actually cuts through the lines of flux.

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4
Q

What is flux density controlled by?

A

The magnitude of the current flowing through the field coils. Normally achieved with a rheostat.

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5
Q

Velocity

A

Controlled by adjusting the speed of the prime mover.

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6
Q

What is Lenz’s Law?

A

The direction of the induced EMF must be such that any current resulting from it will develop a flux that will oppose any change in the original flux.

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7
Q

Flemings Left hand rule

A

insert pic here

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8
Q

What is most commonly used to control generated EMF?

A

Flux density

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9
Q

In Flemings Left hand rule what does the thumb represent?

A

The motion of the conductor.

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10
Q

In Flemings Left hand rule what does the first finder represent?

A

The direction of the magnetic field.

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11
Q

What are the advantages of using AC?

A
  • Alternators can be manufactured with much higher voltage and power ratings than DC.
  • Alternating voltages can be easily stepped up and down.
  • AC motors are generally smaller, simpler cheaper and more reliable than DC.
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12
Q

What are the advantages of using DC?

A
  • Required to produce magnetic fields for alternators and synchronous motors.
  • Electrochemical processes such as electroplating and battery charging require DC.
  • High intensity light sources.
  • precise speed control.
  • DC traction motors.
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13
Q

What is a cycle?

A

The distance from one point on a waveform to where it starts to repeat itself. Consists of 360 degrees.

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14
Q

Alternation

A

One cycle contains two alternations.

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15
Q

What is the period of a waveform?

A

The time it takes to complete one cycle.

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16
Q

Define frequency

A

The number of complete cycles that occur in one second.

17
Q

Peak Value

A

The maximum positive value or negative value of the waveform.

18
Q

How do you find instantaneous value?

A

Einst=Epk x sin angle

19
Q

Average value

A

Epk x .637

20
Q

RMS Value or Effective value

A

Epk x .707

21
Q

What is effective resistance?

A

The property of an electric circuit that dissipates electric energy.

22
Q

What is effective resistance made up of?

A
  • Pure ohmic resistance.
  • Skin effect.
  • Hysteresis losses
  • eddy current losses
  • dielectric losses
  • radiation losses
23
Q

What is the formula for frequency?

A

f= [PxN]/120

24
Q

What is the formula for calculating the time constant of a capacitive circuit.

A

t=RC

25
Q

Where does a capacitor store its energy.

A

In the distortion of the electric fields between its plates.

26
Q

What is the formula for calculating frequency using poles and rpm?

A

f = (P x N) / 120

27
Q

RMS voltage is the same as _______ value

A

Effective value

28
Q

What is electromagnetic induction?

A

The process of generating a voltage by cutting a magnetic field with a conductor.

29
Q

What is the unit of inductance?

A

Henry

30
Q

What are air core inductors?

A

Consist of only wire coils without a core.

Can be found in some high-frequency applications and in some high-voltage protection systems.

31
Q

What are iron-core inductors?

A

Iron-core inductors contain iron or steel in their cores.

32
Q

What are variable inductors?

A

In variable inductors the inductance can be varied by changing the position of the iron relative to the core.

33
Q

What kind of capacitors are self healing??

A

Electrolytic capacitors

34
Q

Capacitance is directly proportional to the

A

Plate area

35
Q

Capacitance in inversely proportional to the

A

Spacing between the plates

36
Q

The capacitance depends on the

A

Type of dielectric between the plates

37
Q

Formula for induced voltage

A

E = -L(

Electrical Year 2 (3 decks)

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