26201-23 Alternating Currents

2:1

What is the step-down turns ratio of a transformer with 50 turns in the primary and 100 turns in the secondary?

induced high voltage

Opening the secondary of a current transformer under load will cause a dangerous level of___.

40Hz

What is the hertz rating of an AC circuit if the frequency is 20 cycles per 1/2 second?

340V

Given: A circuit has an rms voltage of 120VAC. What is the peak-to-peak voltage?

175V

A circuit has a peak voltage of 275V. What is the average voltage value?

one-third the applied voltage

Each of three equal capacitors in series has___.

XL=2piefL

The formula for inductive reactance is___.

10A

Given: An AC circuit containing resistance only. What is the current flow if the resistance is 15 ohms and the voltage is 150v?

Lags the voltage

The current in inductive circuit___.

Rms values

Unless otherwise noted, the calculations in AC circuits use___.

Increases

When frequency decreases, capacitive reactance___.

It leads the voltage.

Which of the following is true of the current in a capacitive circuit?

0.637 x peak value

In sine wave terminology, the average value is___.

All DC rules and laws apply, including Ohm's law

In AC circuits containing only resistance,___.

Increases

If the area of the plates of a capacitor is increased, the amount of capacitance___.

Current with respect to time

The self-induced voltage across in inductance is equal to the change in___.

45

Given: A 30-microfarad capacitor in parallel with a 15-microfarad capacitor. The total capacitance is___.

Inductance

Which of the following opposes any change in circuit current?

Phase relationships that exist between voltage and current in an inductive circuit

"ELI the ICE MAN" is used to remember___.

Greater than the true power

According to the power triangle, the apparent power is___.

Transformer

Which of the following uses electromagnetic induction to transfer electrical energy from one circuit to another?

75V AC

Given: A transformer has 200 turns in the primary, 100 turns in the secondary, and 150V AC applied to the primary. What is the voltage across the secondary?

Unlike-wound transformers

Transformers in which the primary and secondary voltages are 180 out of phase are known as___.

Across the field at 90°

Maximum voltage is generated by rotating wire when the conductor is moving___.

10 Hz

If the time for one cycle is 0.1 second, the frequency is___.

Are in phase

If the phase angles of two sine waves are both 0 degrees then the waves___.

400W

Calculate the true power in a 2A series RL circuit with a 100 ohms resistor.

Frequency increases

Inductive reactance increases as the___.

Apparent power

The power factor can be defined as the ratio of true power to___.

Increasing capacitance

For a given frequency, the capacitive reactance decreases with___.

By some angle between 0° and 90°

In a circuit that has both capacitance and resistance, the current will lead the voltage___.

Are 90° out of phase

If the vector diagram of two AC waveforms is a right angle, then the waves___.

Zero

In an inductive AC circuit, when the applied voltage is at its maximum negative value, the current is___.

Apparent power

The product of the source voltage and the total current is___.

The same as the applied voltage

In a parallel LC circuit, the voltage across the branches is___.

30 microfarads

a 20-microfarad capacitor is in parallel with a 10-microfarad capacitor. The total capacitance is?

half the applied voltage

Each of two equal capacitors in a series has

120VAC

If a transformer has 200 turns in the primary, 100 turns in the secondary, and 240VAC applied to the primary, the voltage across the secondary is?

5hz

If the time for one cycle is .2 seconds, the frequency is?

Sawtooth wave

One type of nonsinusoidal waveform is the

out of phase with true power

Reactive power is always

Iron Core

Transformer windings are typically wrapped around an

Unlike-wound transformers

Transformers in which the primary and secondary voltages are 180 out of phase are known as?

720W

What is the apparent power of an AC circuit with a source voltage of 120V and a total current of 6A?

3600W

what is the apparent power of an AC circuit with a source voltage of 240V and a total current of 15A?

12A

What is the current flow in a purely resistance AC circuit if the resistance is 20ohms and the voltage is 240V?

60hz

What is the frequency of an AC waveform that completes 30 cycles per half second?

3:1

What is the step-down turns ratio of a transformer with 150 turns in the primary and 50 turns in the secondary?

200W

What is the true power in a 2A series RL circuit with a 50ohms resistor?

Frequency

To compare the phase angle between two waves, both waves must have the same

20hz

If a sine wave is repeated 10 time per half-second, it’s frequency is

Oscilloscope

One device that generates a sawtooth waveform is an

220V

What is the voltage(E) in a purely resistive circuit with a current(I) of 22A and 10ohms resistance(R)?

A coil with a short core

Which of the following coils is likely to show the highest inductance?

35UF

The total capacitance of three 10UF capacitors and one 5UF capacitor connected in parallel is

Z

A circuit’s impedance is represented by the letter

Resistance

True power is the product of the resistor current squared and the

Total current

Apparent power is the product of the source voltage and the

Reactive power performs no work

Which of the statements regarding reactive power is correct?

.5

The power factor of a series circuit with a resistance(R) of 75ohms and an impedance(Z) of 150ohms is?

Reactive power

The apparent power is the result of the vector addition of true power and

An iron-core transformer provides better power transfer that an air-core transformer

Which statement regarding transformers is true?

Polarity

On a transformer schematic dots are used to indicate?

60VAC

A transformer has 200 turns in the primary winding, 100 turns in the secondary winding, and 120VAC applied to the primary winding. The voltage across the secondary winding is?

Potential transformer

A voltage-sensing relay is likely to be powered by a?

Magnetic field

An electric current always produces a

Frequency

The number of cycles a waveform produces per second determines the

170VAC

What is the peak voltage in a circuit with an MS voltage of 120VAC?

The voltage and current are in phase

Which of the following conditions exists in a circuit of pure resistance

24V

In a purely resistive AC circuit where 240V is applied across a 10ohm resistor, the amperage is?

It reduces the current

When the current increases in an ac circuit what role does inductance play

A coil with a narrow diameter

Which of the following coils is likely to show the lowest inductance?

The voltage and current are 90 degrees out of phase

Which of the following conditions exists in a circuit of pure inductance?

Farads

Capacitance is measured in

7.5uF

The total capacitance of two 15uF capacitors in series is

30 uF

The total capacitance of two 15uF capacitors connected in parallel is

20uF

The total capacitance of two 5uF capacitors and one 10uF capacitor connected in parallel is

Inductance

Reactance increases with an increase in inductance

Capacitive reactance

The opposition to current flow offered by the capacitance of a circuit is known as

800W

The true power in a circuit with a current of 4A that passes through a 50ohm resistor is

Impedance

The total opposition to current flow in an AC circuit is known as

.5

The power factor in a circuit with a resistance of 50ohms and am impedance of 100ohms is

Cosine of the phase angle

A power factor is not an angular measure, but a numerical ratio with a value between 0 and 1, equal to the

5:1

A transformer with 10 turns in the primary and two turns in the secondary has a turn ratio of

In phase

In a circuit containing resistance only, the voltage and current are _______ with one another.

Resistance

The power consumed by __________ is called true power.

True, Apparent

The power factor is the ratio of ____ power to ____ power

an inductor and a capacitor

LC circuits consist of a(n) ______ and a(n) ______ connected in series or in parallel with a voltage source

Current

As in all series circuits, the ____ in a series LC circuit is the same at all points

50V

On a transformer with 100V applied to the primary winding, 200 turns in the primary winding, and 100 turns in the secondary winding, the secondary voltage is _____ volts

Isolation transformer

A(n) _____ can be used to electrically isolate a piece of equipment from the power distribution system

Voltage source

The primary winding in a transformer is connected to the

Load

The secondary winding is connected to the

Watts

True power is measured in

Reactive

VAR is the unit of measurement for _____ power

True

The average value is calculated from all the values in a sine wave for only half a cycle

0.637

The average value is = ______ x peak value