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