Advertisements
Advertisements
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’.
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.
APPEARS IN
RELATED QUESTIONS
A transformer is designed to convert an AC voltage of 220 V to an AC voltage of 12 V. If the input terminals are connected to a DC voltage of 220 V, the transformer usually burns. Explain.
The AC voltage across a resistance can be measured using
Average power supplied to a capacitor over one complete cycle is ______.
When an ac voltage of 220 V is applied to the capacitor C, then ______.
A capacitor has capacitance C and reactance X, if capacitance and frequency become double, then reactance will be ______.
When an AC voltage of 220 V is applied to the capacitor C ______.
- the maximum voltage between plates is 220 V.
- the current is in phase with the applied voltage.
- the charge on the plates is in phase with the applied voltage.
- power delivered to the capacitor is zero.
In the LCR circuit shown in figure, the ac driving voltage is v = vm sin ωt.
- Write down the equation of motion for q (t).
- At t = t0, the voltage source stops and R is short circuited. Now write down how much energy is stored in each of L and C.
- Describe subsequent motion of charges.
An iron cored coil is connected in series with an electric bulb with an AC source as shown in figure. When iron piece is taken out of the coil, the brightness of the bulb will ______.
An a.c. source generating a voltage ε = ε0 sin ωt is connected to a capacitor of capacitance C. Find the expression for the current I flowing through it. Plot a graph of ε and I versus ωt to show that the current is ahead of the voltage by π/2.
