Alternating current practice · Medium

A $16\,\,\mu F$ capacitor is charged to a $\mathrm{20}\,\,\mathrm{volt}$ potential. The battery is then disconnected and pure $40\,\,mH$ coil is connected across the capacitor so that $\mathrm{LC}$ oscillations are setup. The maximum current in the coil is

For a series $L - C - R$ circuit with $R = 100\,\Omega$, $L = 0.5\mathrm{ mH}$ and $C = 0.1\,\mathrm{pF}$ connected across $\mathrm{220V} - 50\mathrm{ Hz\, AC}$ supply, the phase angle between current and supplied voltage and the nature of the circuit is

Assertion: In series LCR circuit phase difference between current and voltage is never zero.

Reason: Voltage and current are never in phase.

A capacitor of capacitance $100 \, \mu \mathrm{F}$ and a coil of resistance $50 \, \Omega$ and inductance $0.5 \, \mathrm{H}$ are connected in series with a $110 \mathrm{~V}, 50 \mathrm{~Hz}$ AC source. Find the rms value of the current.

A $500 \mu \mathrm{H}$ inductor, $\frac{80}{\pi^2} \mathrm{pF}$ capacitor and a $628 ~\Omega$ resistor are connected to form a series LCR circuit. Calculate the resonant frequency and $Q$-factor of this circuit at resonance

Voltage and current in an ac circuit are given by $V=5 \sin \left(100 \pi t-\frac{\pi}{6}\right)$ and $I=4 \sin \left(100 \pi t+\frac{\pi}{6}\right)$

$A$ radio set operates at $6 \mathrm{~V}$ DC. A transformer with 18 turns in the secondary coil is used to step down the input 220 V AC emf to 6 V AC emf. This AC emf is then rectified by another circuit to give 6 V DC which is fed to the radio. Find the number of turns in the primary.

The power in ac circuit is given by $P = {E_{rms}}{I_{rms}}\cos \phi .$ The value of $\cos \phi$ in series LCR circuit at resonance is

Power factor of series LCR circuit at resonance is

A transformer steps up an A.C. voltage from 230 v to 2300 v. If the number of turns in the secondary coil is 1000, the number of turns in the primary coil will be

By what percent the impedance in an series LCR, AC circuit should be increased so that the power factor changes from $\left( {1/2} \right)$ to $\left( {1/4} \right)\,?$ (assume resistance $R$ remains constant)

Assertion: When capacitive reactance is smaller then the inductive reactance in series LCR circuit, voltage leads the current.

Reason: In series LCR circuit inductive reactance is always greater then capacitive reactance.

A resistance R, inductance L and capacitor C are connected in series to an oscillator of frequency $f$. If resonant frequency is $f$, then current will lag the voltage when

The ratio of secondary to the primary turns in a transformer is $\mathrm{3 : 2}$. If the power output be $P$, then the input power neglecting all losses must be equal to

An ac ammeter is used to measure current in a circuit. When a given direct current passes through the circuit, the ac ammeter reads $3 \mathrm{~A}$. When another alternating current passes through the circuit, the ac ammeter reads $4 \mathrm{~A}$. Then find the reading of this ammeter (in $\mathrm{A}$), if dc and ac flow through the circuit simultaneously.

A solenoid having inductance $4.0 \mathrm{~H}$ and resistance $10 \, \Omega$ is connected to a $4.0 \mathrm{~V}$ battery at $\text{t}=0$. Find

(a) the time constant
(b) the time elapsed before the current reaches 0.63 of its steady-state value

Assertion (A) : Resonance frequency will decrease in $L-C-R$ series circuit if a dielectric slab is inserted in between the plates of the capacitor.

Reason (R) : By doing so, capacity of capacitor will increase.

The power factor of good choke coil is

The value of current in two series $L C R$ circuits at resonance is same. Then

In the circuit with $R = 6\,\,\Omega$ and impedance $10\,\,\,\Omega$. The power factor of circuit is

Find the effective value of current $i=2+4 \cos$ $100 \pi \mathrm{t}$.

Given below are two statements:

Statement I : An AC circuit undergoes electrical resonance if it contains either a capacitor or an inductor.

Statement II: An AC circuit containing a pure capacitor or a pure inductor consumes high power due to its non-zero power factor.

In the light of above statements, choose the correct answer from the options given below:

Assertion (A) : In an $\mathrm{AC}$ circuit, potential difference across the capacitor may be greater than the applied voltage.

Reason (R) : $V_C=I X_C$, whereas $V=I Z$ and $X_C$ can be greater than $Z$ also.

A capacitor, an inductor and an electric bulb are connected in series to an AC supply of variable frequency. As the frequency of supply increased gradually, then the electric bulb is found to be

Power factor of an L-R series circuit is 0.6 and that of a C-R series circuit is 0.5 . If the elements ( $L, C$ and $R$ ) of the two circuit are joined in series the power factor of this circuit is found to be 1. The ratio of the resistance is L-R circuit to the resistance in the C-R circuit is

Assertion: A sinusoidal alternating current does not show any average magnetic effects.

Reason: The average value of an alternating current is zero.

A coil having an inductance of $\frac{1}{\pi}$ henry is connected in series with $300 \Omega$.If $20 \mathrm{~V}$ from a 200 cycle source is impressed across the combination, then the phase angle between, V and $\mathrm{I}$ is-

The instantaneous value of current and emf in an A.C. circuit are $I = \frac{1}{{\sqrt 2 }}\sin 314t$ amp and $E = \sqrt 2 \sin \left( {314t - \frac{\pi }{6}} \right)V,$ with respect to I) will be

There is a current of $20 \mathrm{~mA}$ passing through an ideal inductor when connected to a $100 \mathrm{~V}, 20 \mathrm{~Hz}$ supply. The power consumed is

An alternating current of rms value 10 A passed through 12 ohm resistor. The maximum potential difference across the resistor is [in Volts]