Deck 21: Capacitance in Ac Circuits

Question 1

When a capacitor is connected to a(n) _____ circuit, current appears to flow through the capacitor.

A) DC
B) AC

Answer 1

B

Question 2

What is the reactance of a 25 μ F capacitor when the applied frequency is 400 Hz?

A) 10.61 Ω
B) 11.59 Ω
C) 15.92 Ω
D) 16.12 Ω

Answer 2

C

Question 3

Two capacitors, a 20 μ F and a 30 μ F, are connected in series to a 400 Hz source. What is the total capacitive reactance?

A) 7.96 Ω
B) 33.16 Ω
C) 42.04 Ω
D) 53.05 Ω

Answer 3

B

Question 4

The power in a capacitor is reactive power. What is the unit for reactive power?

A) W
B) VA
C) P
D) VAR

Question 5

In a circuit containing a capacitor, the impressed voltage is _____ with the applied voltage.

A) 180 ° out of phase
B) 90 ° out of phase
C) in phase
D) 270 ° out of phase

Question 6

A 35 μ F capacitor is connected to a 60-Hz, 120 V supply. What is the X_C of the capacitor?

A) 75.79 Ω
B) 80.33 Ω
C) 83.2 Ω
D) 93.43 Ω

Question 7

What is the reactance of a 10 pF capacitor when the applied frequency is 30 Hz?

A) 200.36 Ω
B) 325.76 Ω
C) 530.52 Ω
D) 612.83 Ω

Question 8

The voltage rating of a capacitor _____.

A) can be exceeded as long as the time is under one hour
B) should never be exceeded
C) is only a suggested maximum
D) is a minimum working voltage

Question 9

The quality of a capacitor is found by Q = _____.

A) X_C/R
B) R/X_C
C) PF
D) W/VARs

Question 10

Three capacitors, a 12 ? F, a 20 ? F, and a 30 ? F, are connected in series to a 400 Hz source. What is the total XC ?

A) 36.42 ?
B) 42.78 ?
C) 52.09 ?
D) 66.32 ?

Question 11

The capacitive reactance of a capacitor is _____ proportional to frequency.

A) directly
B) inversely

Question 12

Three capacitors, a 12 μ F, a 20 μ F, and a 30 μ F, are connected in series to a 60 Hz source. What is the total X_C?

A) 226.42 Ω
B) 342.78 Ω
C) 442.09 Ω
D) 566.32 Ω

Question 13

In a pure capacitive circuit, the current _____ the applied voltage by _____.

A) leads; 180 °
B) lags; 180 °
C) leads; 90 °
D) lags; 90 °

Question 14

What is the unit for capacitive reactance?

A) ohm
B) farad
C) henry
D) coulomb

Question 15

​When the voltage and current have _____ polarities in a pure capacitive circuit, the capacitor is discharging and the energy is returned to the circuit.

A) ​the same
B) ​opposite

Question 16

Countervoltage presented by a capacitor is called _____.

A) capacitance
B) inductance
C) capacitive reactance
D) inductive reactance

Question 17

A capacitor is connected to a 240 V supply. An ammeter indicates 3 A. What is the capacitive reactance of the capacitor?

A) 23 Ω
B) 30 Ω
C) 71 Ω
D) 80 Ω

Question 18

What is the symbol for capacitive reactance?

A) C
B) X_C
C) L
D) X_L

Question 19

Two capacitors, a 20 μ F and a 30 μ F, are connected in series to a 60 Hz source. What is the total capacitive reactance?

A) 117.96 Ω
B) 221.04 Ω
C) 253.05 Ω
D) 333.16 Ω

Question 20

A 1 μ F capacitor has 2,652 Ω of reactance at 60 Hz. What is the reactance value at 400 Hz?

A) 397.88 Ω
B) 568.72 Ω
C) 639.79 Ω
D) 768.33 Ω

Question 21

Two capacitors, a 20 μ F and a 30 μ F, are connected in parallel to a 60 Hz source. What is the total capacitive reactance?

A) 7.96 Ω
B) 23.16 Ω
C) 42.04 Ω
D) 53.05 Ω

Question 22

Two capacitors, a 20 μ F and a 30 μ F, are connected in parallel to a 400 Hz source. What is the total capacitive reactance?

A) 7.96 Ω
B) 33.16 Ω
C) 42.04 Ω
D) 53.05 Ω

Question 23

Three capacitors, a 12 μ F, a 20 μ F, and a 30 μ F, are connected in parallel to a 60 Hz source. What is the total X_C?

A) 6.42 Ω
B) 42.78 Ω
C) 442.09 Ω
D) 566.32 Ω

Question 24

Three capacitors, a 12 μ F, a 20 μ F, and a 30 μ F, are connected in parallel to a 400 Hz source. What is the total X_C?

A) 6.42 Ω
B) 42.78 Ω
C) 44.09 Ω
D) 56.32 Ω