2-3) AC-AC Voltage Waveform Flashcards
How many degrees is one cycle of a sine wave?
360 degrees
What is a period equal to?
The duration of time in seconds for one full cycle to complete.
What is the difference between period and frequency?
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.
How do you calculate frequency from the period of a cycle?
Frequency in Hertz = 1 / Period in Seconds
What is the unit of frequency and what does it measure?
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.
What is the standard power line frequency in the US?
60 Hz
What is the standard power line frequency in Europe?
50 Hz
How does an oscilloscope measure frequency?
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
What is the term used to describe any waveshape bearing a close resemblance to a perfect sine wave?
Sinusoidal
What is the term used to describe any waveshape that does not resemble a sine wave?
Non-sinusoidal
What is this wave form?
Sawtooth Wave
What is this wave form?
Sine Wave
What is this wave form?
Square wave
What is this wave form?
Triangle wave
What term is used to describe the intensity or magnitude of a AC wave?
Amplitude
Where on an oscilloscope is amplitude measured?
On the vertical axis
Where on an oscilloscope is frequency or period measured?
On the horizontal axis
What is the term for the point of greatest amplitude on an AC wave?
Peak or crest
What is the measurement of an AC waveform from the greatest positive amplitude to the lowest negative amplitude?
Peak to Peak (P-P)
Why use an average waveform value to compare different AC waves?
Average value is the mathematical mean of all the points. Different wave forms have different voltage amplitudes for different durations.
What does RMS stand for?
Root Mean Squared
What are 2 other terms sometimes used in place of RMS?
“Equivalent” or “DC Equivalent”
What is RMS voltage?
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.
What is the basis for establishing the effective value of alternating current?
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.
What is the basis for establishing the effective value of alternating current?
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.
What measured value is the best way to relate AC to DC quantities?
RMS amplitude
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?
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.
What value of measurement would be most useful when determining the rating of an insulator for service in high-voltage AC applications?
Peak voltage measurements are the most appropriate because the principle concern here is insulator “flashover” caused by brief spikes in voltage, irrespective of time.
