Alternating current practice · Mixed difficulty

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.

In an AC circuit, V and I are given by V = 100 sin [100 t] volts, I = 100 sin $\left[ {100\,t + \frac{\pi }{3}} \right]$ mA. The power dissipated in casuist is [in watt]

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

The ratio of turns in primary and secondary coils of a transformer is 1 : 20. The ratio of currents in primary and secondary coils will be

A bulb is connected first with dc and then ac of same voltage it will shine brightly with

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

A generator produces a voltage that is given by $V = 240\sin 120\;t$ , where t is in seconds. The frequency and r.m.s. voltage are

Find the maximum value of current when a coil of inductance $2 \mathrm{H}$ is connected to $150 \mathrm{~V}$, 50 cycles / sec supply.