Alternating current practice · Mixed difficulty

A resistance of 20 ohms is connected to a source of an alternating potential $V = 220\sin \left[ {100\,\pi \,t} \right]$. The time taken by the current to change from its peak value to r.m.s. value is [in sec]

A bulb and a capacitor are in series with an ac source. On increasing frequency how will glow of the bulb change

An AC circuit having an inductor and a resistor in series draws a power of $560 \mathrm{~W}$ from an AC source marked $210 \mathrm{~V}-60 \mathrm{~Hz}$. The power factor of the circuit is 0.8, the impedance of the circuit and the inductance of the inductor is

Same current is flowing in two alternating circuits. The first circuit contains only inductance and the other contains only a capacitor. If the frequency of the emf of AC is increased, the effect on the value of the current

A resistor R, an inductor L and a capacitor C are connected in series to an oscillator of frequency $n$, if the resonant frequency is ${n_r}$ , then the current lags behind voltage, when

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

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

A series R-C circuit is connected to AC 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 the two cases. Which of the following is/are true?

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

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

In an ideal transformer, the turns ratio is $\frac{N_P}{N_S}=\frac{1}{2}.$ The ratio $V_S: V_P$ is equal to (the symbols carry their usual meaning):

In an L – C – R circuit, capacitance is changed from C to 2C. For the resonant frequency to remain unchanged, the inductance should be changed from L to

In an ideal transformer, the voltage is stepped down from 11 kV to 220 V. If the primary current be 100 A, the current in the secondary should be

In a series $L C R$ circuit, at resonance, the bandwidth frequency can be represented as

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

An ac source of angular frequency $\omega$ is fed across a resistor $r$ and a capacitor $C$ in series. The current in the circuit measured is $l$. If now the frequency of source is changed to $\omega / 3$ (but maintaining the same voltage), the current in the circuit is found to reduce by a factor of three. The power factor of the circuit at the original frequency $\omega$ is

The power factor varies between

The current flowing in a step down transformer 220 V to 22 V having impedance 220 Ω is

An electric bulb has a rated power of 50 W at 100 V. If it is used on an AC source 200 V, 50 Hz, a choke has to be used in series with it. The should have an inductance of

An inductive circuit contains a resistance of 10 ohm and an inductance of 2.0 henry. If an ac voltage of 120 volt and frequency of 60 Hz is applied to this circuit, the current in the circuit would be nearly

In a series $L-C-R$ circuit, $C=10^{-11} \mathrm{~F}, L=10^{-5} \mathrm{H}$ and $R=100 \Omega$, when a constant DC voltage $E$ is applied to the circuit, the capacitor acquires a charge $10^{-9} \mathrm{C}$. The $\mathrm{DC}$ source is replaced by a sinusoidal voltage source in which the peak voltage $E_0$ is equal to the constant $\mathrm{DC}$ voltage $E$. At resonance, the peak value of the charge acquired by the capacitor will be

In an $L C R$ circuit, the resonating frequency is 200 $\,{kHz}$. If the value of $L$ is doubled and value of $C$ is decreased to $\frac{1}{8}$ times of its initial values, then the new resonating frequency in ${kHz}$ will be

The tuning circuit of a radio receiver has a resistance has a resistance of $50\,\,\Omega ,$ an inductance of and $10\,mH$ a variable capacitance $C.\,\,A\,\,1\,\,MHz$ radio wave produces a potential difference of $0.1\,mV.$ The value of capacitance to produce the resonance will be

The sun delivers ${10^3}\,\,w/{m^2}$ of electromagnetic flux incident on a roof of dimensions $8\,\,m\,\, \times \,\,20\,\,m,$ will be

In an LCR circuit R=100 ohm. When capacitance C is removed, the current lags behind the voltage by π/3. When inductance L is removed, the current leads the voltage by π/3. The impedance of the circuit is

The peak voltage of the ac source is equal to:

A resistance of 40 ohm and an inductance of 95.5 millihenry are connected in series in a 50 cycles/second ac circuit. The impedance of this combination is very nearly

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.

In an $LR$-circuit time constant is that time in which current grows from zero to the value (where ${I_0}$ is the steady state current)

Statement (A): The power consumed in an electric circuit is never negative
Statement (B): The average power consumed in an electric circuit is ${P}=\frac{{V}^2}{{R}}={I}^2{R}$

The instantaneous values of current and voltage in an ac circuit are i=100sin⁡ 314 t amp and $e = 200\;in\;\left( {314\;t + \pi /3} \right)V$ , respectively. If the resistance is $1\mathrm{\Omega }$ , then the reactance of the circuit will be