State which of the two a capacitor or an inductor, tends to become SHORT when the frequency of the applied alternating voltage has a high value.
Why is the use of ac voltage preferred over dc voltage ? Give two reasons.
A device ‘X’ is connected to an ac source V = V₀ sin(ωt). The variation of voltage, current and power in one complete cycle is shown in the following figure.
(i) Which curve shows power consumption over a full cycle?
(ii) Identify the device ‘X’.
Why is choke coil needed in the use of fluorescent tubes with ac mains ?
The figure shows two sinusoidal curves representing oscillating supply voltage and current in an ac circuit.
A lamp is connected in series with a capacitor. Predict your observation for dc and ac connections. What happens in each if the capacitance of the capacitor is reduced ?
Show that the current leads the voltage in phase by in an ac circuit containing an ideal capacitor.
An alternating voltage given by V = 140sin314 t is connected across a pure resistor of 50 Find :
(i) the frequency of the source.
(ii) the rms current through the resistor.
Show that in the free oscillations of an LC circuit, the sum of energies stored in the capacitor and the inductor is constant in time.
Obtain the expression for the energy density of magnitude field B produced in the inductor.
(i) Prove that current flowing through an ideal inductor connected across ac source, lags the voltage in phase by .
(ii) An inductor of self inductance 100 mH, and a bulb are connected in series with ac source of rms voltage 10V, 50 Hz. It is found that effective voltage of the circuit leads the current in phase by .Calculate the inductance of the inductor used and average power dissipated in the circuit, if a current of 1 A flows in the circuit.
A device ‘X’ is connected to an ac source V = The variation of voltage, current and power in one cycle is shown in the following graph :
(i) An ac source generating a voltage V = V₀ sin ωt is connected to a capacitor of capacitance C. Find the expression of the current I flowing through it.Plot a graph of V and I versus ωt to show that the current is π/2 ahead of the voltage.
(ii) A resistor of 200Ω and a capacitor of 15 µF are connected in series to a 220 V, 50 Hz ac source.Calculate the current in the circuit and the rms
voltage across the resistor and the capacitor. Why the algebraic sum of these voltages is more than the source voltage ?
A device X is connected across an ac source of voltage V = V₀ sin ωt. The current through X is given as I = I₀sin(ωt +π/2).
(a) Identify the device X and write the expression for its reactance.
(b) Draw graphs showing variation of voltage and current with time over one cycle of ac, for X.
(c) How does the reactance of the device X vary with frequency of the ac ? Show this variation graphically.
(d) Draw the phasor diagram for the device X.
For an ideal conductor, connected across a sinusoidal ac voltage source. State which one of the following quantity is zero :
(i) Instantaneous power
(ii) Average power over full cycle of the ac voltage source.