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