3.1 Flashcards
What is direct current (DC)?
A flow of current where the value and direction remain constant with time/one continual loop.
What is alternating current (AC)?
A flow of current which constantly changes direction and instantaneous value with time.
extra - It changes direction every half cycle.
What device is used to display a.c. waveforms?
an oscilloscope
What two quantities do we want to measure with an oscilloscope?
peak voltage and frequency
What is frequency in terms of alternating current?
The number of waveform cycles in one second
What is the relationship between period and frequency?
T = 1/f
T - period (s)
f - frequency (Hz)
What is the ‘time base’ on an oscilloscope?
allows you to select the rate that waveforms are shown on the screen. This can help measure period.
How do you calculate period for one cycle on an oscilloscope?
T = no. of divisions x timebase
How do you calculate peak voltage of an oscilloscope?
Vp = no. of divisions x y-gain
What is the root mean square?
For a.c. the root mean square is equal to the value of the constant d.c. current that would have the same effect as the a.c. current.
Why is the r.m.s voltage always lower than the peak voltage?
Peak voltage only occurs twice in a cycle, and all other values are lower.
What equation can you use to calculate r.m.s voltage?
Vr.m.s = Vp/ square root 2
What equation is used to calculate r.m.s current?
Ir.m.s = Ip/ square root 2
