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1st 6 Month Final > Electricity 1-7 Ch 3 Review > Flashcards

Electricity 1-7 Ch 3 Review Flashcards

1
Q

AC current ____________ change direction.

A

Periodically

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2
Q

Why is AC used more than DC?

A

Cheaper, easier to distribute to customers, and more versatile

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3
Q

Why is DC not used in transmission?

A

Large power losses

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4
Q

Power/heat loss is directly proportional to ____________ and to the square of ____________.

A

Resistance; current

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5
Q

AC power can be converted, via transformer, to:

A

Various combinations of voltage and current

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6
Q

What device converts AC to various combos of voltage and current?

A

Transformers

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7
Q

Name 2 AC power sources

A

Generators and alternators

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8
Q

AC generators combine ____________ and _________ to produce electricity.

A

Physical motion; magnetism

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9
Q

What is angular motion?

A

Motion in a circle

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10
Q

What does a waveform show?

A

The magnitude and direction of current and voltage at every instance of time

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11
Q

Fluctuating DC waveforms can be the same shape as AC, except…

A

They never go below the horizontal axis

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12
Q

when AV voltage or current goes through 360°, it is said to have completed one __________.

A

Cycle

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13
Q

Current and voltages are _____________ when both reach their min and max values at the same time

A

In-Phase

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14
Q

The peak value of an AC sine wave is equal to ___________.

A

The amplitude or max value of I or E

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15
Q

Equation for effective value of pure sine wave?

A

.707 x peak value

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16
Q

What is used to indicate the time relationship between I and E

A

Phase

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17
Q

The number of cycles generated in one second is the_____________.

A

Frequency

18
Q

In AC, the magnitude of I is directly proportional to _______________.

A

The magnitude of E.

19
Q

The skin effect results in:

A

Higher concentration of current near the surface of the conductor. This reduces the cross-sectional area of the conductor and increases the resistance.

20
Q

What is electric current made up of?

A

Free electrons moving in the same direction

21
Q

The magnitude of induced EMF is directly proportional to 3 things. Name them:

A
  1. Strength of the magnetic field
  2. Length of conductor
  3. Speed the conductor moves through the magnetic field
22
Q

Strength and direction of magnetic field around the conductor through which AC is flowing depends on:

A

Magnitude and direction of current

23
Q

What determines the magnitude of the self induced EMF?

A

Frequency of AC current and its amplitude

24
Q

When current flowing una circuit, the magnetic field holds all of the energy it has taken from the circuit until current begins ____________.

A

Decreasing

25
Q

Why is a greater back EMF produced by self induction if a conductor is coiled?

A

Because flux lines cut the conductor at more than one point.

26
Q

If either inductance or capacitance is present in AC, current flow is __________.

A

Limited

27
Q

______________ oppose all current in a circuit.

A

Resistors

28
Q

Inductive reactance is directly proportional to:

A

Inductance and frequency

29
Q

______________ is the property of an electrical current that tends to oppose any change of current through a circuit.

A

Inductance

30
Q

Inductors are sometimes called:

A

Chokes or coils

31
Q

What is the unit of inductance?

A

Henry

32
Q

A coil is said to be saturated when even large changes in current cannot:

A

Increase the flux

33
Q

Sometimes, on transformer symbols, dots are used to indicate:

A

The in-phase terminal of the two windings

34
Q

If you increase current in a transformer, the current in the primary will ___________.

A

Increase

35
Q

Secondary current is out of phase with primary current by ____°.

A

180

36
Q

A charged capacitor has an electric field that exists between:

A

The plates, and therefore stores energy

37
Q

With all other things held at constant, the capacitance of a capacitor is directly proportional to:

A

The surface area of the plates

38
Q

Voltage across a capacitor lags the current through the capacitor by ___°

A

90

39
Q

In a purely resistive circuit, the power factor equals:

A

1

40
Q

In a purely resistive circuit, the apparent power is equal to:

A

True power

1st 6 Month Final (9 decks)

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