electrical Electrical - AC !
The sine of 0° is___. a. 1 b. -1 c. 0 d. 0.5
0
If the time for one cycle is 0.1 second, the frequency is _______ Hz. a. 0.1 b. 10 c. 0.9 d. 1
10
In an AC circuit containing resistance only,_________ will flow if the resistance is 10 ohms and the voltage is 120V. a. 10A b. 12A c. 16A d. 14A
12A
What is the peak voltage in a circuit with an rms voltage of I20VAC? a. 117 volts b. 120 volts c. 150 volts d. 170 volts
170 volts 120VAC / 0.707 = 170 V
In unlike-wound transformers, the primary and secondary voltages are ____. a. 270° out of phase b. 90° out of phase c. in phase d. 180°out of phase
180°out of phase
The average voltage value in a circuit with a peak voltage of 377V is: a. 170V b. 240V c. 120V d. 108V
240V
In a purely resistive AC circuit where 240V is applied across a l0-ohm resistor, the amperage is a. 10A b. 24A c. 60A d. 120A
24A
The total capacitance of a 20-microfarad capacitor in parallel with a 10-microfarad capacitor is __________ microfarads. a. 30 b. 10 e. 6.67 d. 200
30
The total capacitance of two 15microF capacitors connected in parallel is: a. 5 microF b. 10 microF c. 15 microF d. 30 microF
30 microF
The peak-to-peak voltage in a circuit with an rms voltage of 120VAC is ____. a. 120V b. 340V e. 170V d. 240V
340V
If the frequency of an AC circuit is 15 cycles per 1/4 second, the hertz rating of the circuit is _________. a. 60Hz b. 120Hz c. 30Hz d. 15Hz
60Hz
A transformer has 200 turns in the primary, 150 turns in the secondary, and 120 VAC applied to the primary The voltage across the secondary is ____. a. 100V b. 120V c. 110V d. 90V
90V
When the current increases in an AC circuit, what role does inductance play? a. It increases the current. b. It plays no role at all. c. It causes the overcurrent protection to open. d. It reduces the current.
It reduces the current.
Which of the following conditions exist in a circuit of pure inductance? a. The voltage and current are in phase. b. The voltage and current are 90° out of phase. c. The voltage and current are 120° out of phase. d. The voltage and current are 180° out of phase.
The voltage and current are 90° out of phase.
Which of the following conditions exist in a circuit of pure resistance? a. The voltage and current are in phase. b. The voltage and current are 90° out of phase. c. The voltage and current are 120° out of phase. d. The voltage and current are 180° out of phase.
The voltage and current are in phase.
True or False? Reactance increases with an increase in inductance. a. True b. False
True
The formula for inductive reactance is: a. XL = 2*pi ÷ f*l b. XL = 1 ÷ 2*pi*f*l e. XL = 2 + pi*f*l d. XL = 2*pi*f*l
XL = 2*pi*f*l
An electric current always produces: a. mutual inductance b. a magnetic field c. capacitive reactance d. high voltage
a magnetic field
In AC circuits containing only resistance ______. a. only Ohms law applies b. no DC rules and laws apply c. only Kirchhoff's law applies d. all DC rules and laws apply including Ohms law and Kirchhoff's law
all DC rules and laws apply including Ohms law and Kirchhoff's law
The power triangle shows that the ______ power is greater than the _______ power. a. reactive; apparent b. reactive; true c. apparent; true d. true; apparent
apparent; true
The opposition to current flow offered by the capacitance of a circuit is known as: a. mutual inductance b. pure resistance c. inductive reactance d. capacitive reactance
capacitive reactance
A power factor is not an angular measure, but a numerical ratio with a value between 0 and 1, equal to the _____ of the phase angle. a. sine b. tangent c. cosine d. cotangent
cosine
The phase relationship between voltage and current in a purely capacitive circuit is __________. a. current leads voltage by 90° b. they are in phase c. current leads voltage by 180° d. voltage leads current by 90°
current leads voltage by 90°
In a transformer,_________. a. electromagnetic induction occurs b. voltage is generated in the primary coil c. no magnetic field is present d. capacitance occurs
electromagnetic induction occurs
Capacitance is measured in ____ a. farads b. joules c. henrys d. amps
farads
The number of cycles an alternating electric current undergoes per second is known as: a. amperage b. frequency c. voltage d. resistance
frequency
The total opposition to current flow in an AC circuit is known as: a. resistance b. capacitive reactance c. inductive reactance d. impedance
impedance
If the area of the plates of a capacitor is increased, the amount of capacitance __________. a. may increase b. decreases c. increases d. stays the same
increases
When frequency decreases, capacitive reactance ____. a. increases b. decreases c. may increase or decrease d. stays the same
increases
The secondary of a CT under load should not he opened because of ______. a. induced high voltage b. low impedance c. induced high current d. high impedance
induced high voltage
When the coil turns are increased, the _______. a. additional turns oppose the circuit resistance b. induced voltage is increased c additional turns oppose the induced voltage d. induced voltage is decreased
induced voltage is increased
In an inductive circuit, the current _____ voltage. a. lags b. in the same as C. counteracts d. leads
lags
All of the following factors increase the inductance of a coil, except a: a. greater number of turns b. longer core c. wider coil d. magnetic core
longer core
Each of three equal capacitors in series has _______ the applied voltage. a. one-third b. three times c. the original value of d. one-half
one-third
Inductance ________. a. increases only in DC circuits b. opposes any change in circuit current c. aids any change in circuit current d. takes no action when a change in circuit current occurs
opposes any change in circuit current
The two windings of a conventional transformer are known as the ____ windings. a. mutual and inductive b. high and low voltage c. primary and secondary d. step-up and step-down
primary and secondary
Meters used in AC circuits indicate the ________ value. a. reactive b. inflective c. peak d. rms
rms
Unless otherwise noted, the calculations in AC circuits use _____ values. a. phase b. rms c. median d. peak
rms
A transformer with a primary or 400 turns and a secondary of 300 turns has a ______. a. step-down turns ratio of 4:3 b. step-up turns ratio of 3:4 c. step-up turns ratio of 4:3 d. step—down turns ratio of 3:4
step-down turns ratio of 4:3
The self-induced voltage across an inductance L is produced by a change in current with respect to _________. a. distance b. time c. field d. width
time