Alternating current practice · Mixed difficulty

An electric bulb and a capacitor are connected in series with an AC source. On increasing the frequency of the source, the brightness of the bulb:

Maximum power is dissipated in an LCR circuit at resonance

In L – C – R series circuit the resonance condition in terms of capacitive reactance $\left( {{X_C}} \right)$ and inductive reactance $\left( {{X_L}} \right)$ is

For a given AC source the average emf during the positive half cycle

A coil of inductance $0.50 \mathrm{~H}$ and resistance $100 \Omega$ is connected to a $240 \mathrm{~V}, 50 \mathrm{~Hz}$ ac supply. What are the maximum current in the coil and the time lag between voltage maximum and current maximum?

Average power in the L-C-R circuit depends upon

In a series L-R circuit, under which condition the power loss will be least for an a.c. voltage source?

The primary coil of an ideal transformer has 100 turns and secondary coil has 200 turns. Then select the correct option.

The peak power consumed by a resistive coil when connected to an AC source is 80 W. Find the energy consumed by the coil in 100 seconds which is many times larger than the time period of the source.

The phase difference between the alternating current and emf is $\pi / 2$. Which of the following cannot be the constituent of the circuit?

A transformer has an efficiency of $80 \%$. It works at $4 \mathrm{~kW}$ and $100 \mathrm{~V}$. If secondary voltage is $240 \mathrm{~V}$, the current in primary coil is

The electric current in a circuit is given by $[i=3 \sin \omega t+4 \cos \omega t]$. The value of $rms$ current is:

Assertion: In series LCR circuit resonance can take place.

Reason: Resonance takes place if inductance and capacitive reactances are equal and opposite.

An emf $E=4 \cos 1000 \mathrm{t}$ volt is applied to an L-R circuit of inductance $3 \mathrm{mH}$ and resistance $4 \Omega$. The amplitude of the current in the circuit is

An ac source of angular frequency ω is fed across a resistor r and a capctior C in series. The current registered is $I$. If the frequency of source is changed to ω/3 (maintaining the same voltage), the current in the circuit is found to be halved. Calculate the ratio of reactance to resistance at the original frequency ω

When the current in an ac circuit is wattles, the phase difference between the applied voltage and circuit current will be

Given below are two statements.

Statement I: In an ac circuit, the current through a capacitor
leads the voltage across it.

Statement II: In a.c circuits containing pure capacitance only,
the phase difference between the current and
the voltage is $\pi.$

In the light of the above statements, choose the
most appropriate answer from the options
given below.

A particle oscillating under a force $\overrightarrow F = - k\overrightarrow x - b\overrightarrow v$ is a [K and b are constants] :

Assertion (A) : In series $L-C \cdot R$ circuit, if a ferromagnetic rod is inserted inside an inductor, current in the circuit may increase or decrease.

Reason (R) : By doing so $X_L$ will increase.

The primary winding of a transformer has 200 turns and its secondary winding has 50 turns. If the current in the secondary winding is 40 A, the current in the primary is

In a series LCR circuit, the voltages across an inductor, a capacitor, and a resistor are $30{~V}, 30{~V}$ and $60{~V}$ respectively. The phase difference between the applied voltage and the current in the circuit is

An a.c current is given by $i=3 \sin w t+4 \cos w t$ amp. Its rms value is

An $L-C$ circuit is in a state of resonance. If $C=0.1 \mu \mathrm{F}$ and $L=0.25 \mathrm{H}$, then neglecting the ohmic resistance of the circuit, find the frequency of oscillations.

A series $R-C$ circuit is connected to $A C$ voltage source. Consider two cases; $(A)$ When $C$ is without a dielectric medium and $(B)$ When $C$ is filled with dielectric of constant 4 . The current $I_R$ through the resistor and voltage $V_C$ across the capacitor are compared in two cases. Which of the following is true?

The core of any transformer is laminated so as to

A resistor of resistance $400 ~\Omega$, and a capacitor of reactance $200 ~\Omega$, are connected in series to a $220 \mathrm{~V}, 50 \mathrm{~Hz}$, a.c. source. If the current in the circuit is 0.49 ampere, find the (i) voltage across the resistor and capacitor (ii) value of inductance required so that voltage and current are in phase.

In an ac circuit with voltage V and current I, the power dissipated is

In an AC circuit the instantaneous values of emf and current are $e = 200\sin 300\;t\;\mathrm{volt}$ and $i = 2\sin \left( {300t + \frac{\pi }{3}} \right)$ amp. The average power consumed in watt is

A current of $2 \mathrm{~A}$ is flowing at $220 \mathrm{~V}$ in the primary coil of a transformer. If current in the secondary coil is $1 \mathrm{~A}$ and efficiency of the transformer is $80 \%$ then the voltage produced in the secondary coil will be

Which is not true for series LCR circuit in resonance: