2-3) AC-AC Voltage Waveform

Question 1

How many degrees is one cycle of a sine wave?

Answer 1

360 degrees

Question 2

What is a period equal to?

Answer 2

The duration of time in seconds for one full cycle to complete.

Question 3

What is the difference between period and frequency?

Answer 3

Period and frequency are mathematical reciprocals of one another. That is to say, if a wave has a period of 10 seconds, its frequency will be 0.1Hz, or 1/10 of a cycle per second.

Question 4

How do you calculate frequency from the period of a cycle?

Answer 4

Frequency in Hertz = 1 / Period in Seconds

Question 5

What is the unit of frequency and what does it measure?

Answer 5

Frequency is the rate of back and forth oscillation and it is measured in the unit Hertz. Hertz represents the number of complete wave cycles completed during 1 second of time.

Question 6

What is the standard power line frequency in the US?

Answer 6

60 Hz

Question 7

What is the standard power line frequency in Europe?

Answer 7

50 Hz

Question 8

How does an oscilloscope measure frequency?

Answer 8

The period of the waveform (the time in seconds it takes to complete one full cycle) is measured on the horizontal axis. The period is reciprocated to determine the frequency in Hertz.

Example:
Frequency = 1 / period = 1 / 16ms = 62.5 Hz

Question 9

What is the term used to describe any waveshape bearing a close resemblance to a perfect sine wave?

Answer 9

Sinusoidal

Question 10

What is the term used to describe any waveshape that does not resemble a sine wave?

Answer 10

Non-sinusoidal

Question 11

What is this wave form?

Answer 11

Sawtooth Wave

Question 12

What is this wave form?

Answer 12

Sine Wave

Question 13

What is this wave form?

Answer 13

Square wave

Question 14

What is this wave form?

Answer 14

Triangle wave

Question 15

What term is used to describe the intensity or magnitude of a AC wave?

Answer 15

Amplitude

Question 16

Where on an oscilloscope is amplitude measured?

Answer 16

On the vertical axis

Question 17

Where on an oscilloscope is frequency or period measured?

Answer 17

On the horizontal axis

Question 18

What is the term for the point of greatest amplitude on an AC wave?

Answer 18

Peak or crest

Question 19

What is the measurement of an AC waveform from the greatest positive amplitude to the lowest negative amplitude?

Answer 19

Peak to Peak (P-P)

Question 20

Why use an average waveform value to compare different AC waves?

Answer 20

Average value is the mathematical mean of all the points. Different wave forms have different voltage amplitudes for different durations.

Question 21

What does RMS stand for?

Answer 21

Root Mean Squared

Question 22

What are 2 other terms sometimes used in place of RMS?

Answer 22

“Equivalent” or “DC Equivalent”

Question 23

What is RMS voltage?

Answer 23

RMS is the “effective value” of AC. This is the value of alternating voltage or current that will have the same effect on a resistance as a comparable value of direct voltage or current will have on the same resistance.

Question 24

What is the basis for establishing the effective value of alternating current?

Answer 24

The rate at which heat is produce in a resistance forms a convenient basis for establishing an effective value of alternating current, and is known as the heating effect.

An alternating current is said to have an effective value of 1A when it produces heat on a given resistance at the same rate as does 1A of direct current.

Question 24

What is the basis for establishing the effective value of alternating current?

Answer 24

The rate at which heat is produce in a resistance forms a convenient basis for establishing an effective value of alternating current, and is known as the heating effect.

An alternating current is said to have an effective value of 1A when it produces heat on a given resistance at the same rate as does 1A of direct current.

Question 25

What measured value is the best way to relate AC to DC quantities?

Answer 25

RMS amplitude

Question 26

What value measurement would be most useful when determining the proper size of a wire (amp capacity) to conduct electric power from a source to a load?

Answer 26

RMS current measurement is the best to use because the principle concern with current is overheating of the wire. Wire heating is a function of power dissipation cause by current through the wire’s resistance.

Question 27

What value of measurement would be most useful when determining the rating of an insulator for service in high-voltage AC applications?

Answer 27

Peak voltage measurements are the most appropriate because the principle concern here is insulator “flashover” caused by brief spikes in voltage, irrespective of time.