The figure below shows an oscilloscope screen capture of a periodic signal. The

Question

The figure below shows an oscilloscope screen capture of a periodic signal. The oscilloscope settings are: time scale = 5 s/div and voltage scale = 50 V/div. What are the frequency and the maximum voltage for the signal shown? The minimum value of the signal is 0V-----------------------------"The figure below shows an oscilloscope screen capture of a sine wave periodic signal. The oscilloscope settings are: horizontal time scale = 5 s/div and vertical voltage scale = 50 V/div. One cycle of the sine wave covers 4 division in the horizontal axis and 2 divisions in the positive vertical axis and 2 divisions in the negative vertical axis."

Explanation / Answer

From Ohms law: V=I xR, the voltage across the capacitor depends upon the current 'passing through' the capacitor multiplied by its 'resistance'. However, the resistance depends upon the frequency and for this reason the resistance is given a special name called reactance; in particular the capacitive reactance. This capacitive reactance then depends upon the frequency and so the voltage across the capacitance is also frequency dependent. The higher the frequency the lower will be the capacitive reluctance and the lower the voltage across the capacitor will be. In fact, if the frequency is high enough the capacitive reactance may be so low as to be like a short circuit (the equiv. of a piece of wire).

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