Alternating current practice · Medium

Statement (A): An electric lamp is connected in series with a long solenoid of copper with air core and then connected to AC source. If an iron rod is inserted in solenoid the lamp will become dim.

Statement (B): If iron rod is inserted in solenoid, the induction of solenoid increases.

Alternating current cannot be measured by DC ammeter because

An AC source rated $100 \mathrm{~V}$ (rms) supplies a current of $10 \mathrm{~A}$ (rms) to a circuit. The average power delivered by the source:

A $100\,\Omega$ resistance and a capacitor of $100\,\Omega$ reactance are connected in series across a $200\,{\mkern 1mu} V$ source. When the capacitor is 50% charged, the peak value of the displacement current is

Impedance of a coil having inductance 0.4 H at frequency of 50 Hz will be

A portable generator turning at $350\, \mathrm{rad} / \mathrm{s}$ produces an EMF of $120 \mathrm{~V}\, \mathrm{rms}$. If an additional $500 \mathrm{~W}$ light bulb is added to the circuit, what additional torque is required to keep the generator spinning at $350 \,\mathrm{rad} / \mathrm{s}$ ?

Assertion: Chock coil is preferred over a resistor to adjust current in an ac circuit.

Reason: Power factor for inductance is zero.

An alternating current in a circuits is given by $I = 20\sin \left[ {100\,\pi \,t + 0.05\pi } \right]A$. The rms value and the frequency of current respectively are

A.C power is transmitted from a power house at a high voltage as

The number of turns in primary and secondary coils of a transformer are $\mathrm{100}$ and $\mathrm{20}$ respectively. If an alternating potential of $200\,\,volt$ is applied to the primary, the induced potential in secondary will be

Find the value of $t / \tau$ for which the current in an LR circuit builds up to

(a) $90 \%$, (b) $99 \%$ and (c) $99.9 \%$ of the steady-state value.

An A.C. source is connected to a resistive
circuit. Which of the following is true?

The power is transmitted from a power house on high voltage ac because

A coil of inductance L has an inductive reactance of ${X_L}$ in an AC circuit in which the effective current is $I$. The coil is made from a super-conducting material and has no resistance. The rate at which power is dissipated in the coil is

When the speed of a dc motor increases the armature current

An alternating voltage $\mathrm{V}=\mathrm{V}_0$ sin $\omega \mathrm{t}$ is applied across a circuit. As a result, a current $\mathrm{I}=\mathrm{I}_0 \sin (\omega t-\pi / 2)$ flows in it. The power consumed per cycle is

When power is drawn from the secondary coil of the transformer, the dynamic resistance

For an $L C R$ series circuit with an ac source of angular frequency $\omega$,

Statement (A): Maximum power is dissipated in a circuit (through R ) in resonance.

Statement (B): At resonance in a series LCR circuit, the voltage across indcutor and capacitor are out of phase.

Assertion: In higher power transmission, $240 \mathrm{~V}$ is preferred over $120 \mathrm{~V}$.
Reason: Power loss is more in case of 120 Vas compared to 240 V.

Assertion (A) : An inductor coil normally produces more current with DC source compared to an AC source of same value of rms voltage.

Reason (R) : In DC source, applied voltage remains constant with time.

Assertion: The alternating current lags behind the e.m.f. by a phase angle of $\pi / 2$, when ac flows through an inductor.

Reason: The inductive reactance increases as the frequency of ac source decreases.

The square root of the product of inductance and capacitance has the dimension of

In a LCR oscillatory circuit find the energy stored in inductor at resonance, if voltage of source is $10 \mathrm{~V}$ and resistance is $10 \,\Omega$ and inductance is $1 \,\mathrm{H}$.

Assertion (A) : In series $L-C \cdot R$ circuit, voltage will lead the current function for frequency greater than the resonance frequency.

Reason (R) : At resonance frequency, phase difference between current function and voltage function is zero.

Assertion (A)If the frequency of the applied $AC$ is doubled, then the power factor of a series $R-L$ circuit decreases.

Reason (R) Power factor of series R-L circuit s given' by

$\cos \theta=\frac{2 {R}}{\sqrt{{R}^2+\omega^2 {~L}^2}}$

Which type of losses donot occur in the transformer?

What is the average power dissipation in an ideal capacitor in an AC circuit?

A capacitor of $10 \mu \mathrm{F}$ and an inductor of $1 \mathrm{~H}$ are joined in series. An ac of $50 \mathrm{~Hz}$ is applied to this combination. What is the impedance of the combination?

In step-up transformer, relation between number of turns in primary $\left( {{N_p}} \right)$ and number of turns is secondary $\left( {{N_s}} \right)$ coils is