Alternating current practice · Mixed difficulty

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)

In an AC circuit, the instantaneous values of emf and current are e=200sin⁡314t volt and $I = \sin \left( {314t + \frac{\pi }{3}} \right)\,amp$ , The average power consumed in watt is

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

The instantaneous values of current and emf in an ac circuit are $I = 1/\sqrt 2$ $\sin 314\;t\;amp$ and $E = \sqrt 2 \sin \left( {314\;t - \pi /6} \right)V$ respectively. The phase difference between E and I will be

In an AC series circuit, the instantaneous current is maximum when the instantaneous voltage is maximum. The circuit element connected to the source will be

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, ${e^2}\, = \,7.389$)

An alternating e.m.f. is applied to purely capacitive circuit. The phase relation between e.m.f. and current flowing in the circuit is or
In a circuit containing capacitance only

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-

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.

What is the value of inductance L for which the current is a maximum in a series L-C-R circuit with $C = 10\mu \mathrm{F}$ and $\omega = 1000\;{\mathrm{s}^{ - 1}}?$

Alternating current cannot be measured by DC ammeter because

For a series R-L-C circuit:

(a) Voltage across L and C differ by $\pi$ phase

(b) Current through L and R are in same phase

(c) Voltage across R and L differ by $\pi/2$ phase

(d) Voltage across L and current through C differ by $\pi/2$ phase

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

In an ac circuit, the instantaneous current is zero, when the instantaneous voltage is maximum. In this case, the source may be connected to:
A. pure inductor.
B. pure capacitor.
C. pure resistor.
D. combination of an inductor and capacitor.
Choose the correct answer from the options given below: