Alternating current practice · Mixed difficulty

What is the self-inductance of a coil which produces 5 V when the current changes from 3 A to 2 A in one millisecond?

Statement (A): The reactance offered by an inductance in A.C. circuit decreases with increase of A.C frequency.

Statement (B): The reactance offered by a capacitor in A.C circuit increases with increase of A.C frequency.

A series LCR circuit is connected to an ac voltage source. When $\mathrm{L}$ is removed from the circuit, the phase difference
between current and voltage is $\frac{\pi }{3}$. If instead $\mathrm{C}$ is removed from the circuit, the phase difference is again $\frac{\pi }{3}$ between
current and voltage. The power factor of the circuit is:

In AC circuit a resistance of R Ω is connected in series with an inductance L. If the phase difference between the current and voltage is 45°, the inductive reactance will be

Statement (A): In high current low voltage windings of a transformer thick wire is used to minimize energy loss due to heat produced.

Statement (B): The core of any transformer is laminated so as to reduce the energy loss due to eddy currents.

A LCR circuit is at resonance for a capacitor C, inductance $\mathrm{L}$ and resistance $\mathrm{R}$. Now the value of resistance is halved keeping all other parameters same. The current amplitude at resonance will be now:

Choke coil is used to control

An AC source producing emf

$e=e_0\left[\cos \left(100 \pi \mathrm{s}^{-1}\right) t+\cos \left(500 \pi \mathrm{s}^{-1}\right) t\right]$

is connected in series with a capacitor and resistor. The steady state current in the circuit is found to be

$I=I_1 \cos \left[\left(100 \pi \mathrm{s}^{-1}\right) t+\phi_1\right]+I_2 \cos \left[\left(500 \pi \mathrm{s}^{-1}\right) t+\phi_2\right]$

A $9 / 100 \pi$ inductor and a $12 \Omega$ resistance are connected in series to a $225 \mathrm{~V}, 50 \mathrm{~Hz}$ ac source. Calculate the current in the circuit and the phase angle between the current and the source voltage.

In an LCR series AC circuit, the voltage across each of the components, L, C and R is 50 V. the voltage across the LC combination will be

Assertion: With increase in frequency of an A.C supply, the impedance of an L-C-R series circuit, decreases at first, becomes minimum and then increases.

Reason: In L-C-R series circuit, impedance (z)
$z=\sqrt{R^2+\left(X_L-X_C\right)^2}$.

In a step-up transformer, the turn ratio is $\mathrm{1 : 2}$. A Leclanche cell (e.m.f. $\mathrm{1}\mathrm{.5}\,\,\mathrm{V}$) is connected across the primary. The voltage developed in the secondary would be

The transformation ratio in the step-up transformer is

The household supply of electricity is at $220 \mathrm{~V}$ (rms value) and $50 \mathrm{~Hz}$. Find the peak voltage and the least possible time in which the voltage can change from the rms value to zero.

A capacitor of capacitance $1 \mu \mathrm{F}$ is charged to a potential of $1 \mathrm{~V}$. It is connected in parallel to an inductor of inductance $10^{-3} \mathrm{~H}$. The maximum current that will flow in the circuit has the value

An AC source of variable frequency is applied across a series L-C-R circit . At a frequency double the resonance frequency. The impedance is $\sqrt{10}$ times the minimum impedance. The inductive reactance is

A series LCR circuit is connected to an ac voltage source. When $\mathrm{L}$ is removed from the circuit, the phase difference
between current and voltage is $\frac{\pi }{3}$. If instead $\mathrm{C}$ is removed from the circuit, the phase difference is again $\frac{\pi }{3}$ between
current and voltage. The power factor of the circuit is:

The power dissipated in an AC circuit is zero if the circuit is

Alternating current in circuit is given by $I=I_0 \sin 2 \pi$ nt. Then the time taken by the current to rise from zero to r.m.s. value is equal to

The average power dissipation in a pure capacitance in AC circuit is:

A transformer operating at primary voltage $8 \mathrm{kV}$ and secondary voltage $160 \mathrm{~V}$ serves a load of $80 \mathrm{~kW}$. Assuming the transformer to be ideal with purely resistive load and working on unity power factor, the loads in the primary and secondary circuit would be

Find the maximum value of current when an inductance of one henry is connected to an a.c. source of 200 volts, $50 \mathrm{~Hz}$

Statement (A): If current varies sinusoidally the average power consumed in a cycle is zero.

Statement (B): If current varies sinusoidally the average current is zero in a complete cycle.

When $100 \mathrm{V} \mathrm{~DC}$ is applied across a coil, a current of $4 \mathrm{~A}$ flows through it. When $200 \mathrm{V} \mathrm{AC}$ at $100 \mathrm{~Hz}$ is applied to the same coil, a current of amplitude $\sqrt{2}$ A flows. The reactance of the coil is

An inductor and a resistor are connected in series with an ac source. In this circuit.

An inductance of $0.05 / \pi$ Henry and a 12 ohm resistance with resistance (negligible) are connected in series combination. Across the end of this electric circuit is connected a $130 \mathrm{~V}$ alternating voltage of frequency 50 cycles/second. Find out the alternating current in the circuit and potential difference across the inductance and that across the resistance.

The instantaneous values of voltage and current in an ac circuit are represented by $V = 2\sqrt 2 \sin \left( {100\pi t + \frac{\pi }{4}} \right)$ $i = \frac{1}{{\sqrt 2 }}\sin 100\pi t$. The angular frequency of ac is

The phase difference between the current and voltage of LCR circuit in series combination at resonance is

Which of the following quantities remains constant in a step-down transformer ?

Statement (A): With increase in frequency of $\mathrm{AC}$ supply inductive reactance increases.

Statement (B): With increase in frequency of $\mathrm{AC}$ supply capacitive reactance increase