Chapter 6 - Alternating Current Flashcards
What is the peak value of an alternating current?
The maximum current which is the same in either direction. Same for peak pd.
What is the time period for a 50Hz alternating supply?
T = 1/f = 0.02 seconds.
What is the root mean square value of an alternating current?
The value of direct current that would give the same heating effect as the alternating current in the same resistor. This is found by peak value divided by square root of 2.
How is the mean power from an alternating supply calculated?
Either rms current squared x resistance OR
rms voltage squared divided by resistance OR
rms current x rms voltage.
What does the x axis on an oscilloscope trace represent?
The time base.
What does the y axis on an oscilloscope trace represent?
The pd of the supply.
Describe the oscilloscope trace of an ad supply with the time base switched off.
A straight vertical line showing the peak to peak voltage.
Describe how you would measure the time base of an ax supply from an oscilloscope trace.
Measure the time over as many whole cycles as possible, then divide that by the number of cycles.
Describe the oscilloscope trace of a dc supply when the time base is switched off.
A dot on the screen at a height corresponding to the pd of the supply.
Describe the oscilloscope trace of a dc supply when the time base is switched on.
A straight horizontal line at a pd corresponding to the power source (assuming no internal resistance)
How can you determine the peak pd of a supply from an oscilloscope trace?
Measure the vertical displacement from the zero line to the highest point on the trace then multiplying this with the y gain (given in V cm-1)
If a waveform on an oscilloscope trace is 2.6cm long and the time base is 4ms cm-1 what is the frequency of the supply?
2.6 x 0.004 = 0.0104
Then 1/0.0104 = 96Hz
Define the frequency of an alternating current.
The number of cycles it passes through each second. Measured in Hertz.
