Alternating Current

A 220 volts input is supplied to a transformer. The output circuit draws a current of 2.0 ampere at 440 volts. If the efficiency of the transformers is 80%, the current drawn by the primary windings of the transformer is

A coil has resistance 30 ohm and inductive reactance 20 ohm at 50 Hz frequency. If an ac source, of 200 volt, 100 Hz, is connected across the coil, the current in the coil will be

A coil of self-inductance L is connected in series with a bulb B and an AC source. Brightness of the bulb decreases when

An a.c. supply gives 30 volt r.m.s which passes through a 10Ω resistance. The power dissipated in it is

The frequency of an alternating voltage is 50 cycles per second and its amplitude is 120 V. Then the r.m.s. value of voltage is

A filament bulb (500 W,100 V) is to be used in a 230 V main supply. When a resistance R is connected in series, it works perfectly and the bulb consumes 500 W. The value of R is

Which of the following combinations should be selected for better tuning of an L-C-R circuit used for communication?

The potential differences across the resistance, capacitance and inductance are 80 V, 40 V and 100 V respectively in an L-C-R circuit. The power factor of this circuit is

A 100Ω resistance and a capacitor of 100 Ω reactance are connected in series across a 220 V source. When the capacitor is 50% charged, the peak value of the displacement current is

A small signal voltage V(t) = V₀ sin ωt is applied across an ideal capacitor C

An inductor 20 mH, a capacitor 50 μF and a resistor 40Ω are connected in series across a source of emf V=10 sin 340t. The power loss in AC circuit is

An alternating voltage given as, V = 100√2 sin 100t V is applied to a capacitor of 1 μF. The current reading of the ammeter will be equal to …….. mA

An inductor coil is connected to a 12 V battery and drawing a current 24 A. This coil is connected to capacitor and an AC source of rms voltage rating 24 V in the series connection. The phase difference between current and emf is zero. The rms current through the circuit would found to be

In a circuit, the current lags behind the voltage by a phase difference of π/2. The circuit contains which of the following?

The electric current in AC circuit is given by the relation i-3 sinωt+4 cosωt. The rms value of the current in the circuit in ampere is

In an L-C-R series resonant circuit, the capacitance is changed from C to 4C. For the same resonant frequency, the inductance should be changed from L to

In a circuit, L,C and R are connected in series with an alternating voltage source of frequency f. The current leads the voltage by 45⁰. The value of C is

The average power dissipated in a pure inductor is

Transformer is used to

A step-up transformer operates on a 230 V line and supplies a current of 2 A. The ratio of primary and secondary winding is 1:25. The primary current is

A step-down transformer has 50 turns on secondary and 1000 turns on primary winding. If a transformer is connected to 220 V, 1 A AC source, then what is output current of the transformer?

The primary and secondary coil of the transformer have 50 and 1500 turns respectively. If the magnetic flux ɸ linked with the primary coil is given by ɸ = ɸ₀ + 4t, where ɸ is in webers, t is time in seconds and ɸ₀ is the constant, the output voltage across the secondary coil is

In L-C-R series circuit, an alternating emf e and current i are given by the equations e=100 sin (100t) V.
i=100 sin⁡(100t+π/3)mA .
The average power dissipated in the circuit will be

A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 amp, the efficiency of the transformer is approximately

The average power dissipated in AC circuit is 2 W. If a current flowing through a circuit is 2 A, impedance is 1Ω, then what is the power factor of the circuit?

What is the value of incidence L for which the current is maximum in a series LCR circuit with C = 10 µF and ? = 1000 s⁻¹?

In an a.c circuit the e.m.f. (e) and the current (i) at any instant are given respectively by
e = E₀ sin ωt
i = I₀ sin (ωt – ɸ)
The average power in the circuit over one cycle of a.c. is

An alternating emf given by equation
e = 300 sin ⁡[(100 π)t] V
is applied to a resistance 100Ω. The rms current through the circuit is (in amperes)

Power dissipated in an LCR series circuit connected to an a.c source of emf ε is

The alternating current in a circuit is given by I=50 sin 314 t. The peak value and frequency of the current are

Weber ampere per metre is equal to

An ac voltage is applied to a resistance R and an inductor L in series. If R and the inductive reactance are both equal to 3Ω, the phase difference between the applied voltage and the current in the circuit is

If the alternating current I = I₁ cos ωt+I₂ sin ⁡ωt, then the rms current is given by

In an ac circuit an alternating voltage e = 200 √2 sin 100 t volts is connected to a capacitor of capacity 1 µF. The r.m.s. value of the current in the circuit is

For a transformer, the turns ratio is 3 and its efficiency is 0.75. The current flowing in the primary coil is 2A and the voltage applied to it is 100 V. Then the voltage and the current flowing in the secondary coil are ……. Respectively.

The voltage of an a.c.supply varies with time (t) as V = 120 sin 100 πt cos 100 πt the maximum voltage and frequency are respectively

In R-L-C series circuit, the potential differences across each element is 20 V. Now the value of the resistance alone is doubled, then PD across R,L and C respectively.

The instantaneous values of alternating current and voltages in a circuit are given as
i = 1/√2 sin (100πt) ampere
e = 1/√2 sin (100πt + π/3) Volt
The average power in Watts consumed in the circuit is:

If both the resistance and the inductance in an LR AC series circuit are doubled the new impedance will be

If an A.C. mains supply is given to be 220 V, what would be the average e.m.f. during a positive half cycle?

The primary of a transformer when connected to a dc battery of 10 volt draws a current of 1mA. The number of turns of the primary and secondary windings are 50 and 100 respectively. The voltage in the secondary and the current drawn by the circuit in the secondary are respectively

Alternating current is transmitted to distant places at

For a series L-C-R circuit, the rms values of voltage across various components are Vʟ = 90 V, Vᴄ = 60V and Vʀ = 40 V. The rms value of the voltage applied to the circuit is

An air core coil and an electric bulb are connected in series with an AC source. If an iron rod is put in the coil, then the intensity of light of the bulb will

The power factor of an AC circuit having resistance R and inductance L connected in series to an AC source of angular frequency ω is

The self-inductance of a choke coil is 10 mH. When it is connected with a 10 V DC source, then the loss of power is 20 W. When its is connected with 10 V AC source loss of power is 10 W. The frequency of AC source will be

If in a L-R series circuit the power factor is 1/2 and R=100Ω, then the value of L is, when AC mains is used

In an electrical circuit R,L,C and an AC voltage source are all connected in series. When L is removed from the circuit, the phase difference between the voltage and the current in the circuit is π/3. if instead, C is removed from the circuit, the phase difference is again π/3. The power factor of the circuit is

A transformer of 100% efficiency has 200 turns in the primary coil and 40000 turns in secondary coil. It is connected to a 220 V main supply and secondary feeds to a 100 kΩ resistance. The potential difference per turn is

An electric motor runs on DC source of emf 200 V and draws a current of 10 A. If the efficiency be 40%, then the resistance of armature is

The wing span of an aeroplane is 20 m. It is flying in a field where the vertical component of magnetic field of earth is 5 x 10⁻⁵ tesla with velocity 360 km/hour. The potential difference produced between the blades will be

Eddy currents are used in

The rms current in an AC circuit is 2 A. If the wattless current be √3 A, what is the power factor of the circuit?

In a LCR series circuit, the potential difference between the terminals of the inductor is 60 V, between the terminals of the capacitor is 30 V and that across the resistance is 40 V. Then, supply voltage will be equal to

An inductor is connected to an a.c. source when compared to voltage, the current in the lead wires

An alternating voltage of 220 V, 50 Hz frequency is applied across a capacitor of capacitance 2 μF. The impedence of the circuit is

An LCR circuit contains resistance of 100 ohm and a supply of 200 volt at 300 radian angular frequency. If only capacitance is taken out from the circuit and the rest of the circuit is joined, current lags behind the voltage by 60⁰. If on the other hand, only inductor is taken out the current leads by 60⁰ with the applied voltage. The current flowing in the circuit is

In a series resonant LCR circuit, the voltage across R is 100 volts and R =1kΩ with C= 2 μF. The resonant frequency ω is 200 rad/s. At resonance the voltage across L is

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

Two tangent galvanometers A and B have coils of radii 8 cm and 16 cm respectively and resistance 8 Ω each.They are connected in parallel with a cell of emf 4 V and negligible internal resistance. The deflections produced in the T.G’s A and B are 30⁰ and 60⁰ respectively. If A has 2 turns, then B must have

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

In the series resonance the value of impedence is 3 Ω and the resistance is 4Ω, then the value of power factor of the circuit is

An electric lamp is connected to 220 V, 50 Hz supply. Then the peak voltage is

In an AC circuit the potential differences across an inductance and resistance joined in series are respectively 16 V and 20 V. The total potential difference of the source is

An ideal coil of 10 H is connected in series with a resistance of 5Ω and a battery of 5 V. 2 second after the connection is made, the current flowing in ampere in the circuit is

An alternating voltage e = 200 s in 100t is applied to a series combination of R= 30Ω and an inductor of 400 mH. The power factor of the circuit is