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'A' Level Questions - The Oscilloscope

Q2. An alternating current (a.c.) source is connected to a resistor to form a complete circuit. The trace obtained on an oscilloscope connected across the resistor is shown below. The oscilloscope settings are: Y sensitivity 4.0V per division, time base 1.0 ms per division.

Remember that an oscilloscope is a voltmeter that plots you a voltage time graph on the screen. In an exam mark on the values from the settings so that you can interpret the information easily.

On this screen you can easily determine the period of one period directly - usually, to calculate a period you would usually find the time for several full oscillations and then divide by the number of periods - this cuts down error.

(a) Determine the peak voltage of the a.c. source.

8V

(b) Hence calculate the r.m.s. voltage.

Vrms = V0 /

= 8/

= 5.7V

(c) Determine the time period of the a.c. signal.

T = 3 ms

(d) Hence calculate the frequency of the a.c. signal.

f = 1/T = 1/(3 x 10-3) = 330 Hz

(Total 4 marks)