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Flashcards in aC Electrical Deck (39)
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What is alternating current ?

A form of current electricity where the polarity of the source periodically changes

1

Three forms of AC?

Square wave, triangle tooth, sine wave.

2

Describe square wave?

Polarity periodically changes but value does not

3

Describe triangle tooth?

Polarity periodically changes, value changed with straight line variation.

4

Describe sine wave?

Polarity periodically changes, value changes based on sine function

5

Generation of sine AC?

Created through the principle of electromagnetic induction.

6

Definition of electromagnetic induction?

The creation of an electrical potential in a conductor by passing that conductor through lines of magnetic flux

7

What's the difference between magnetic induction and electromagnetic induction?

Magnetic induction used an actual magnet

8

Polarity if the potential is based on what two things?

The orientation of the lines of flux, the direction the conductor is cutting the lines of flux.

9

How is the polarity of the potential determined?

By the left hand rule.

10

What is the left hand rule?

Point first finger in the direction of the lines of flux, point thumb in direction of conductor movement, middle finger will point in the direction of current flow.

11

Two ways of increasing potential?

Increase the strength of the flux field being cut, increase the rate at which the lines of flux are being cut.

12

Ways to increase the strength of the flux field?

Increase current flow through the electromagnet
Increase the density of the lines of flux

13

Ways to increase the rate at which lines of flux are cut?

Increase the speed of the conductor
Increase the number of conductors cutting the flux

14

Advantages of AC over DC?

Much easier to generate large quantities of, much easier to change values without substantial power loss, much easier to transfer over long distances.

15

Disadvantage of AC?

Not as efficient as DC.

16

What is a cycle?

One complete sequence of events from zero to the negative peak and back to zero

17

What is an alternation?

One half of a cycle, in either the positive or negative direction

18

What is a period?

The time required for one cycle to occur, measured in seconds.

19

What is frequency?

The number of cycles per second,
Measured in hertz.

20

Important thing to remember about period and frequency?

The are inverses of each other.

21

Formula for frequency?

(# of poles)(RPM)
-------------------
120

22

What is a phase?

The positional relationship between the current and voltage with respect to when each is increasing and decreasing.

23

What is in phase?

An immediate increase in either current or voltage coincides with an immediate increase in the other

24

What is out of phase?

Any condition other than in phase

25

Phase shift?

The amount of current and voltage are out of phase, in degrees of conductor rotation.

26

Lead or lag?

Tells which changes first, given with respect of current.

27

What is the most out of phase something can be?

90°

28

What is apparent power?

The amount of power that would be dissipated in a DC circuit, apparent power is not an actual power, it is measured in volt amps.

29

Formula for apparent power?

P=IxE