Alternating current practice · Medium

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.

An alternating current is given by the following equation: $I=3 \sqrt{2} \sin (100 \pi t+\pi / 4)$. Give the frequency and rms value of the current.

The primary and secondary coils of a transformer have $\mathrm{50}$ and $\mathrm{1500}$ turns respectively. If the magnetic flux $\phi$ linked with the primary coil is given by $\phi = {\phi _0} + 4\mathrm{t}$, where $\phi$ is in weber, $t$ is time in second and ${\phi _0}$ is a constant, the output voltage across the secondary coil is

Statement (A): An inductor, capacitor and resistance connected in series. The combination is connected across AC source. Peak current through each remains same.

Statement (B): Average power delivered by source is equal to average power consumed by resistance.

If ${E_0}$ is the peak emf, ${I_0}$ is the peak current and $\phi$ is the phase difference between them, then the average power dissipation in the circuit is

A generator at a utility company produces $\mathrm{100 A}$ of current at $\mathrm{4000}\,\,\mathrm{V}$. The voltage is stepped up to $\mathrm{240000}\,\,\mathrm{V}$ by a transformer before it is sent on a high voltage transmission line. The current in transmission line is

Assertion: An electric lamp connected in series with a variable capacitor and ac source, its brightness increases with increase in capacitance.

Reason: Capacitive reactance decrease with increase in capacitance of capacitor.

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)

The impedance of a circuit consists of 3 ohm resistance and 4 ohm reactance. The power factor of the circuit is

The current and emf through an inductance differ in phase by.

When 100 volt DC source is applied across a coil, a current of 1 A flows through it. When 100 V AC source of 50 Hz is applied to the same coil, only 0.5 A current flows. Calculate the inductance of the coil

The hysteresis cycle for the material of a transformer core is

The turn ratio of a transformer is $\mathrm{1:2}$. An electrolytic DC cell of emf $\mathrm{2 V}$ is connected to its primary. The output voltage across transformer is

A coil has an inductance of $1 H$. (i) At what frequency will it have a reactance of $3142 \Omega$ ? (ii) What should be the capacity of a capacitor which has the same reactance at that frequency?

In an AC generator, a coil with N turns, all of the same area A and total resistance R, rotates with frequency $\omega \,$ in a magnetic field B. The maximum value of emf generated in the coils is

An emf of 20 V is applied at time $t = 0$ to a circuit containing in series 10 mH inductor and $5\,\Omega$ resistor. The ratio of the currents at time $t\, = \,\infty$ and at $t\, = \,40\,s$ is close to (Take, ${e^2}\, = \,7.389$)

A 0.7 henry inductor is connected a cross a 120 V- 60 Hz ac source. The current in the inductor will be very nearly (in amp)

Assertion: Average power loss in series LC circuit is always zero.

Reason: Average values of voltage and current in A. C. is zero.

A transformer with efficiency $80 \%$ works at $4 \mathrm{~kW}$ and $100 \mathrm{~V}$. If the secondary voltage is $200 \mathrm{~V}$, then the primary and secondary currents are respectively-