Ch4 Inductive and capacitive reactance Flashcards Preview

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Flashcards in Ch4 Inductive and capacitive reactance Deck (31):
1

What effect does an inductor have on a change in current?

An inductor opposes a change in current.

2

What is the phase relationship between current and voltage in an inductor?

Current lags voltage by 90º (ELI).

3

What is the term for the opposition an inductor presents to ac?

Inductive reactance.

4

. What is the formula used to compute the value of this opposition?

XL = 2πfL.

5

What happens to the value of XL as frequency increases?

XL increases.

6

What happens to the value of XL as inductance decreases?

XL decreases.

7

. What effect does the capacitor have on a changing voltage?

The capacitor opposes any change in voltage.

8

What is the phase relationship between current and voltage in a capacitor?

Current leads voltage by 90º (ICE).

9

. What is the term for the opposition that a capacitor presents to ac?

Capacitive reactance.

10

What is the formula used to compute this opposition?

X=1/2pieX(F)X(C)

11

What happens to the value of XC as frequency decreases?

XC increases.

12

What happens to the value of XC as capacitance increases?

XC decreases.

13

What is the formula for determining total reactance in a series circuit where the values of XC and
XL are known?

X = XL - XC or X = XC - XL

14

. What is the total amount of reactance (X) in a series circuit which contains an XL of 20 ohms and
an XC of 50 ohms? (Indicate whether X is capacitive or inductive)

30 Ω (capacitive).

15

What term is given to total opposition to ac in a circuit?

Impedance.

16

What formula is used to calculate the amount of this opposition in a series circuit?

Z=Rsquared +Xsquared under check

17

What is the value of Z in a series ac circuit where XL = 6 ohms, XC = 3 ohms, and R = 4 ohms?

Z = 5Ω.

18

What are the Ohm's law formulas used in an ac circuit to determine voltage and current?

E=IZ I=E/Z

19

What is the true power in an ac circuit?

True power is the power dissipated in the resistance of the circuit or the power actually used in
the circuit

20

What is the unit of measurement of true power?

watt

21

What is the formula for calculating true power?

True Power = (IR) squared R.

22

What is the reactive power in an ac circuit?

Reactive power is the power returned to the source by the reactive components of the circuit

23

What is the unit of measurement for reactive power?

var.

24

What is the formula for computing reactive power?

reactive power=(Ix)squaredX

25

What is apparent power?

The power that appears to the source because of circuit impedance, or the combination of true
power and reactive power.

26

What is the unit of measurement for apparent power?

VA (volt-amperes).

27

What is the formula for apparent power?

(true power)squared + (reactive power)squared under check

28

What is the power factor of a circuit?

PF is a number representing the portion of apparent power actually dissipated in a circuit

29

What is a general formula used to calculate the power factor of a circuit?

PF=True power/apparent power

30

An ac circuit has a total reactance of 10 ohms inductive and a total resistance of 20 ohms. The
power factor is .89. What would be necessary to correct the power factor to unity?

Add 10 ohms of capacitive reactance to the circuit.

31

What is the difference between calculating impedance in a series ac circuit and in a parallel ac
circuit?

In a series circuit impedance is calculated from the values of resistance and reactance. In a
parallel circuit, the values of resistive current and reactive current must be used to calculate total
current (impedance current) and this value must be divided into the source voltage to calculate the
impedance.