Chapter 15 Alternating Voltage and Current

What is the wavelength in meters of an electromagnetic radio wave whose frequency is 850 MHz? Round the final answer to the nearest hundredth.

0.35

decade

10:1 range in frequencies; representing frequency multiples.

Calculate the rms value of a sine wave with a peak value of 24V. Round the final answer to the nearest whole number.

17

For a sine wave of alternating voltage, how many degrees are included for 1/2 cycle? 360° 90° 180° 270°

180°

Identify the characteristics of a sine wave of voltage. 1. The waveform changes its values slowest when it is at its minimum value. 2. The waveform changes its values fastest when it crosses the zero axis. 3. The cycle includes 360° or 2π rad. 4. The polarity reverses each half-cycle. 5. The maximum values are at 180° and 360°.

2. The waveform changes its values fastest when it crosses the zero axis. 3. The cycle includes 360° or 2π rad. 4. The polarity reverses each half-cycle.

Calculate the period T for the sine wave frequency of 350 Hz. Round the final answer to the nearest tenth.

2.9

The peak value of a sine wave equals 42 V. Calculate the instantaneous voltage of the sine wave for the phase angle of 30°. Round the final answer to the nearest whole number.

21

What is the frequency f of a sine wave that completes 4500 cycles per second? Round the final answer to the nearest whole number in Hz.

4500

Identify the degrees included for 1/4 cycle of a sine wave of alternating voltage. 360° 180° 90° 270°

90°

In a motor, what connects to the electrical source that drives the motor? Solenoid Coil Armature Switching contacts

Armature

A sine wave of alternating voltage crosses the zero axis at 90° in the entire cycle. True False

False

An oscilloscope cannot measure or display the peak-to-peak values of an ac waveform. True False

False

The full-cycle of revolution is also called an alternation. True False

False

The numerical value of π is 1.314. True False

False

When the amplitude of a sine wave is measured with an ac voltmeter, the value displayed by the meter will be the average value. True False

False

Which of the following is an advantage of ac over dc power? Higher voltages available Greater efficiency in distribution More popular in electronic circuits Higher currents available

Greater efficiency in distribution

Which of the following is not an advantage of three-phase ac voltage? More efficient distribution of power Induction motors are self-starting Ripple is easier to filter Less complicated configurations

Less complicated configurations

A sine wave is proportional to the sine of an angle of rotation in the circular motion producing the voltage. True False

True

Alternating voltage continuously varies in amplitude and periodically reverses polarity. True False

True

One complete revolution of a waveform is called a cycle. True False

True

The dc value of a waveform is its average value over one complete cycle. True False

True

The peak value is the maximum value of a sine wave. True False

True

The rms value of a sine wave is equal to 0.707 times peak value. True False

True

To compare the phase relationship between two ac sine waves, both sine waves must have exactly the same frequency. True False

True

octave

a common unit for frequency multiples

The half-cycle of revolution is called a(n) harmonic cycle alternation pulse

alternation

average value

arithmetic average of all values in one half cycle (full cycle average= 0)

transformer

can only operate with alternating current to step up or step down an ac voltage; an apparatus for reducing or increasing the voltage of an alternating current.

vertical position

conductors cut across the flux and produce maximum voltage.

motor

converts electricity into rotary motion.

generator

converts mechanical energy into electric energy.

alternating current

current that varies continuously in magnitude and reverse in polarity; current whose magnitude changes continuously with time and direction changes periodically.

One complete revolution of an ac waveform is a(n) harmonic cycle alternation pulse

cycle

harmonic frequency

exact multiples of the fundamental frequency

The number of cycles per second is the frequency measured in maxwells siemens hertz gilberts

hertz

phasors

indicates the amplitude and phase angle of ac voltage and current.

Radian (rad)

is an angle equivalent to 57.3 degrees.

phase angle

is the angular difference between the same points on two different waves of the same frequency.

grounding

is the practice of connecting gone side of the power line to earth or the ground.

peak value

maximum value Vm or Im, this applies to the positive or negative peak.

cycle

one complete revolution of the loop around the circle; measurement between two successive points having the same value and direction; the variations between two successive points having the same value and varying in the same direction; can be defined as including the variations between two successive points having the same value and varying in the same direction.

The amount of time it takes for one cycle is called the ______________.

period

The symbol for a ______________ angle is θ.

phase

root means square (RMS) or effective value

relates the amount of sine wave of voltage or current to the DC values that will produce the same heating effect.

Current variations are in phase with the applied voltage in an ac circuit with capacitors only inductors only resistors only resistors, capacitors, and inductors

resistors only

conductor loop

rotates through the magnetic field to generate induced ac voltage across open terminals.

sine wave

sinusoidal wave or sinusoid is a voltage waveform.

sonic frequencies

sound waves in the audible frequency range

inductance

the ability of a conductor to produce induced voltage when the current applies.

Wavelength

the distance a wave travels in one cycle

alternation

the half cycle of a revolution

horizontal position

the loop does not induce a voltage because the conductors do not cut across the flux.

power line (or mains)

the main line for the parallel branches

hertz (Hz)

the measurement of frequency

frequency (f)

the number of cycles per second

velocity (v)

the speed of something in a given direction; can be influenced by electromagnetic fields, air pressure; it is the time rate of change in angular displacement.

period (T)

the time per cycle

The amount of induced voltage is proportional to the sine of the angle of rotation in the circular motion production the voltage. true false

true

peak to peak

usually but not always double the peak value as it measures distance between two amplitudes.

sound waves

variations in pressure generated by mechanical vibrations rather than electrical

alternating voltage

voltage that varies continuously in magnitude and reverses in polarity; any voltage that varies in both magnitude and polarity with respect to time.

ultrasonic waves

waves above the audible range of frequencies

Y (wye)

windings in the form of a y

delta

windings in the shape of a triangle