Alternating current practice · Mixed difficulty

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

Statement I: The power factor of an inductor is zero.

Statement II: In the inductor, the emf and current differ in phase by $\frac{\pi}{2}$.

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

Transformer is based upon the principle of

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?

The peak value of house hold line voltage is

Find the output voltage of an ideal transformer connected to a $220 \mathrm{~V}$ A.C and number of turns in primary coil and secondary coil of transformer are 100 and 10 respectively.

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

When capacitor is connected to the circuit, the current, when key is pressed, is

Statement I : In a series $L-C$ - $R$ circuit, the resonance can take place.

Statement II : Resonance takes place, if the inductive and capacitive reactances are equal and opposite.

A $100 \mu \mathrm{F}$ capacitor in series with a $40 ~\Omega$ resistance is connected to a $110 \mathrm{~V}, 60 \mathrm{~Hz}$ supply. What is the maximum current in the circuit?

In a series $L R$ circuit $X_L=R$ and power factor of the circuit is $P_1$. When capacitor with capacitance $C$ such that $X_L=X_C$ is put in series, the power factor becomes $P_2$. The ratio $\frac{P_1}{P_2}$ is

An ideal choke takes a current of 10 ampere when connected to an A.C. supply of 125 volt and $50 \mathrm{~Hz}$. A pure resistor under the same conditions takes a current of 12.5 ampere. If the two are connected to an A.C. supply of $100 \sqrt{2}$ volt and 40 hertz, then find the current in a series combination of the above resistor and inductor.

$Q$-factor can be increased by having a coil of:

A choke coil has negligible resistance. The alternating potential drop across it is 220 volt and the current is 5mA. The power consumed is.