Monitoring and Measuring a.c. Flashcards Preview

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Flashcards in Monitoring and Measuring a.c. Deck (15)
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1
Q

what is direct current?

A

a one-way flow of electrons from negative to positive terminals of a power supply. Produced by chemical cells and batteries.

2
Q

what is alternating current?

A

electrons change direction back and forth in the conductor. Produced in UK power station for mains electricity.

3
Q

what is the frequency of mains voltage?

A

50Hz

a wave is completed 50 times a second

4
Q

what is an oscilloscope used for?

A

to display a.c. waveforms

5
Q

what is the y-axis on an oscilloscope?

A

the voltage across a component

6
Q

what is the x-axis on an oscilloscope?

A

shows how voltage changes over time.

7
Q

what 2 values can be determined using an oscilloscope?

A
  1. frequency

2. peak voltage

8
Q

definition of frequency

A

number of cycles of the waveform in one second

9
Q

how is frequency calculated using an oscilloscope?

A

using the time taken for one cycle (period)
period is measured using the ‘timebase’ of the oscilloscope
f=1/T

10
Q

how is peak voltage determined using an oscilloscope?

A

the maximum vertical deviation of the trace from the central line is measured
this number of divisions is multiplied by the Y gain

11
Q

what is the r.m.s. voltage of an a.c. signal equal to?

A

the value of direct current which would have the same effect or energy change as the a.c.

12
Q

which is always higher: peak or r.m.s. voltage?

A

peak voltage

13
Q

what does r.m.s stand for?

A

Root of the
Mean of the
Square of the voltage

14
Q

equation to work out rms voltage

A

Vrms=Vpeak/ root 2

15
Q

equation to work out rms current

A

Irms=Ipeak/ root 2