Deck 24: Alternating Current Circuits

Question 1

The ______________ power in watts can be calculated as I²R.

Answer 1

real

Question 2

A ______________ does not dissipate power but stores energy in an electric or magnetic field.

Answer 2

reactance

Question 3

The power factor is a numerical ratio with a value between 0 and 1 equal to the ______________ of the phase angle.

Answer 3

cosine

Question 4

When V and I are out of phase because of reactance, the product of V times I is called ______________ power.

Question 5

The D'Arsonval moving coil type meter ______________ read if it is used in an ac circuit.

Question 6

All ______________ ac meters have scales calibrated in rms values unless noted otherwise on the meter.

Question 7

The ______________ uses fixed coils to measure current in a circuit, and the moving coil measures voltage.

Question 8

The _____________ resultant of branch currents is the total line current.

Question 9

For _____________ inductors, the branch currents can be added algebraically.

Question 10

For a series RLC circuit, Z_T can be _____________ either X_L or X_C alone.

Question 11

What can be calculated as I²R?

A) Real power
B) Apparent power
C) Reactive power
D) Power factor

Question 12

In a circuit with resistance and reactance, real power can be calculated as

A) IR
B) VI
C) VI cos q
D) R²I

Question 13

Resistive power that is dissipated as heat is

A) real power
B) apparent power
C) reactive power
D) VAR

Question 14

What does not dissipate power but stores energy in an electric or magnetic field?

A) Resistance
B) Reactance
C) Reluctance
D) Impedance

Question 15

What indicates the resistive component and is the power factor for a resistive / reactive circuit?

A) Cos ?
B) Sin ?
C) Tan ?
D) Cotan ?

Question 16

What is a numerical ratio with a value between 0 and 1 that is equal to the cosine of the phase angle?

A) Reactance factor
B) Power factor
C) Resistance factor
D) Phase factor

Question 17

Unity power factor means a

A) resistive circuit
B) reactive circuit
C) series circuit
D) parallel circuit

Question 18

When V and I are out of phase because of reactance, the product of V times I is called

A) real power
B) true power
C) approximate power
D) apparent power

Question 19

Volt-amperes at the angle of 90° are called

A) watts
B) VA
C) VARs
D) joules

Question 20

In order to realize efficient distribution of electric power in commercial applications, the power factor should be close to

A) 0
B) 1
C) 63.7
D) 45

Question 21

Which of the following meter movements will not read properly in an ac circuit?

A) Thermal type
B) Electromagnetic type
C) D'Arsonval type
D) Rectifier type

Question 22

Which of the following meter movements use a heating effect of the current, which is independent of polarity?

A) Rectifier type
B) Thermal type
C) Electromagnetic type
D) D'Arsonval type

Question 23

The wattmeter is an example of what type meter movement?

A) Rectifier type
B) Thermal type
C) Electromagnetic type
D) D'Arsonval type

Question 24

Which of the following is not affected by changing frequencies?

A) Resistance
B) Inductive reactance
C) Capacitive reactance
D) Impedance

Question 25

Which of the following does not always have the same phase angle?

A) R
B) V_R
C) X_L
D) I_R

Question 26

In parallel circuits I_L and I_C have opposite phase angles, the result is

A) a single net reactive line current
B) two reactive line currents
C) total current less resistive current
D) increased impedance

Question 27

In a resistor

A) V leads I
B) I leads V
C) V and I are always in phase
D) V and I are never in phase

Question 28

X_L is a phasor quantity with a

A) 45° phase angle
B) 90° phase angle
C) 0° phase angle
D) 180° phase angle

Question 29

The voltage across any capacitive reactance always lags its capacitive charge and discharge current by

A) 45°
B) 90°
C) 120°
D) 180°

Question 30

Opposite reactive branch currents are

A) 0° out of phase with each other
B) 45° out of phase with each other
C) 90° out of phase with each other
D) 180° out of phase with each other

Question 31

The impedance angle of the series circuit is the angle whose

A) tangent equals X/R
B) tangent equals R/X
C) cosine equals X/R
D) sine equals R/X

Question 32

In general, when the series resistance and reactance are equal, Z_{T is}

A) 1.414 times either value
B) 0.707 times either value
C) the arithmetic sum of R and X
D) 63.7% of either value

Question 33

In using double subscripts, the first letter in the subscript is the

A) ground reference
B) point of measurement with respect to the second letter
C) out of phase reference
D) in phase reference

Question 34

In a parallel circuit, q is the angle whose

A) tangent equals I_X/IR
B) tangent equals I_R/IX
C) cosine equals I_X/IR
D) cosine equals I_R/IX

Question 35

In a parallel circuit, ? is the angle whose

A) tangent equals I_X/I_R
B) tangent equals I_R/I_X
C) cosine equals I_X/I_R
D) cosine equals I_R/I_X

Question 36

Volt-amperes at the angle of 90° are called

A) watts
B) VA
C) VARs
D) joules

Question 37

In series circuits, X_L is at 90° and X_C is at -90° which are opposite phase angles.

Question 38

Since parallel circuits with I_L and I_C have opposite phase angles, their phasor currents oppose each other and result in a single net reactive line current.

Question 39

In a resistor, V and I are always out of phase.

Question 40

X_L is a phasor quantity with a 90° phase angle.

Question 41

For series inductors, the voltage drops can be added algebraically, since each voltage drop has the same phase relationship with respect to the series current.

Question 42

With regard to the phase angle for the capacitive reactance, the voltage across any X_C always leads its capacitive charge and discharge current by 90°.

Question 43

In a circuit with both X_L and X_C, the opposite phase angles enable one to offset the effect of the other.

Question 44

Exactly opposite reactive branch currents are 180° out of phase with each other.

Question 45

Total R and net X can be added by phasors to find the total ohms of opposition in an entire series circuit.

Question 46

For a series RLC circuit, Z_T can be less than either X_L or X_C alone.

Question 47

The impedance angle of a series circuit is the angle whose tangent equals X/R.

Question 48

In general, when the series resistance and reactance are equal, Z_T is 1.414 times either value.

Question 49

In using double subscripts, note that the first letter in the subscript is the point of measurement with respect to the second.

Question 50

For a parallel RLC circuit, I_T can be less than either I_L or I_C alone.