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Question
A device ‘X’ is connected to an a.c source. The variation of voltage, current and power in one complete cycle is shown in figure.
- Which curve shows power consumption over a full cycle?
- What is the average power consumption over a cycle?
- Identify the device ‘X’.
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Solution
(a) Power is the product of voltage and current (Power = P = VI).
So, the curve of power will be having a maximum amplitude, equal to the product of amplitudes of voltage (V) and current (I) curve. Frequencies, of B and C are equal, therefore they represent V and I curves. So, curve A represents power.
(b) The full cycle of the graph (as shown by the shaded area in the diagram) consists of one positive and one negative symmetrical area.
Hence, average power consumption over a cycle is zero.
(c) Here phase difference between V and I is π/2 therefore, the device ‘X’ may be an inductor (L) or capacitor (C) or the series combination of L and C.
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