A resistance of 20 ohms is connected to a source of an alternating potential V = 220 sin(). The time taken by the current to change from its peak value to r.m.s value is :
1. 0.2 sec
2. 0.25 sec
3.
4.
The potential difference V and the current i flowing through an instrument in an ac circuit of frequency f are given by volts and I = 2 sin ωt amperes (where ω = 2πf). The power dissipated in the instrument is
(1) Zero
(2) 10 W
(3) 5 W
(4) 2.5 W
The impedance of a coil, when DC supply is replaced by AC supply:
1. will remain the same
2. will increase
3. will decrease
4. will be zero
A generator produces a voltage that is given by V = 240 sin 120 t, where t is in seconds. The frequency and r.m.s. voltage are
(1) 60 Hz and 240 V
(2) 19 Hz and 120 V
(3) 19 Hz and 170 V
(4) 754 Hz and 70 V
In an ac circuit, the current is given by and the ac potential is V = 200 sin(100t) volt. Then the power consumption is :
(1) 20 watts
(2) 40 watts
(3) 1000 watts
(4) 0 watt
A resistance of \(20~ \mathrm{ohms}\) is connected to a source of an alternating potential, \(V=220sin(100 \pi t).\) The time taken by the current to change from its peak value to its r.m.s value will be:
1. | \( 0.2~ \mathrm{sec}\) | 2. | \( 0.25~ \mathrm{sec}\) |
3. | \(25 \times10^{-3}~ \mathrm{sec}\) | 4. | \(2.5 \times10^{-3}~ \mathrm{sec}\) |
A resistance of 300 Ω and an inductance of henry are connected in series to an ac voltage of 20 volts and a 200 Hz frequency. The phase angle between the voltage and current will be:
1.
2.
3.
4.
In a LCR circuit having L = 8.0 henry, C = 0.5 μF and R = 100 ohm in series. The resonance frequency in radian per second is
(1) 600 radian/second
(2) 600 Hz
(3) 500 radian/second
(4) 500 Hz
The phase difference between the current and voltage of LCR circuit in series combination at resonance is
(1) 0
(2) π/2
(3) π
(4) –π
In a series LCR circuit, resistance R = 10Ω and the impedance Z = 20Ω. The phase difference between the current and the voltage is
(1) 30°
(2) 45°
(3) 60°
(4) 90°
In an ac circuit the reactance of a coil is \(\sqrt{3}\) times its resistance, the phase difference between the voltage across the coil to the current through the coil will be:
1. \(
\pi / 3
\)
2. \( \pi / 2
\)
3. \( \pi / 4
\)
4. \( \pi / 6\)
The capacity of a pure capacitor is 1 farad. In dc circuits, its effective resistance will be
(1) Zero
(2) Infinite
(3) 1 ohm
(4) 1/2 ohm
In an LCR circuit, the potential difference between the terminals of the inductance is 60 V, between the terminals of the capacitor is 30 V and that between the terminals of the resistance is 40 V. The supply voltage will be equal to:
1. 50 V
2. 70 V
3. 130 V
4. 10 V
In an LR-circuit, the inductive reactance is equal to the resistance R of the circuit. An e.m.f. applied to the circuit. The power consumed in the circuit is:
(1)
(2)
(3)
(4)
In the circuit given below, what will be the reading of the voltmeter
(1) 300 V
(2) 900 V
(3) 200 V
(4) 400 V
For a series RLC circuit, R = XL = 2XC. The impedance of the circuit and phase difference between V and i will be:
1.
2.
3.
4.
In the adjoining ac circuit the voltmeter whose reading will be zero at resonance is
(1) V1
(2) V2
(3) V3
(4) V4
In the adjoining figure, the impedance of the circuit will be:
(1) 120 ohm
(2) 50 ohm
(3) 60 ohm
(4) 90 ohm
In a series LCR circuit, which one of the following curves represents the variation of impedance (Z) with frequency (f)?
1. | 2. | ||
3. | 4. |
The variation of the instantaneous current (I) and the instantaneous emf (E) in a circuit are shown in the figure. Which of the following statements is correct?
1. | The voltage lags behind the current by π/2. |
2. | The voltage leads the current by π/2. |
3. | The voltage and the current are in phase. |
4. | The voltage leads the current by π. |
The figure shows the variation of R, XL, and XC with frequency f in a series L, C, R circuit. Then for what frequency point, the circuit is inductive:
(1) A
(2) B
(3) C
(4) All points
An ac source of variable frequency f is connected to an LCR series circuit. Which one of the graphs in the figure represents the variation of the current I in the circuit with frequency f :
(1)
(2)
(3)
(4)
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
(a) 230 (b) 46
(c) 26 (d) 13
The potential differences across the resistance, capacitance and inductance are 80 V, 40 V and 100 V respectively in an L-C-R circuit.
What is the power factor of this circuit?
1. 0.4
2. 0.5
3. 0.8
4. 1.0
An inductor 20 mH, a capacitor 50μF, and a resistor 40Ω are connected in series across a source of emf V=10sin340t. The power loss in the AC circuit is:
1. 0.67 W
2. 0.78W
3. 0.89 W
4. 0.46 W
A series R-C circuit is connected to an alternating voltage source. Consider two situations:
1. When the capacitor is air-filled.
2. When the capacitor is mica filled.
Current through the resistor is I and voltage across the capacitor is V then
(1)Va<Vb
(2)Va>Vb
(3)ia>ib
(4)Va=Vb
The instantaneous values of alternating
current and voltages in a circuit are given
as
The average power in Watts consumed in the
circuit is
(a)
(b)
(c)
(d)
In an AC circuit an alternating voltage volt is connected to a capacitor The value of the current in the circuit is
(a) 100 mA
(b) 200 mA
(c) 20 mA
(d) 10 mA
In AC circuit the emf (e) and the current (i) at any instant are given respectively by
The average power in the circuit over one cycle of AC is
(1)
(2)
(3)
(4)
Given below are two statements:
Assertion (A): | In transistor common emitter mode as an amplifier is preferred over common base mode. |
Reason (R): | In common emitter mode the input signal is connected in series with the voltage applied to the base emitter junction. |
1. | Both (A) and (R) are true and (R) is the correct explanation of (A). |
2. | Both (A) and (R) are true but (R) is not the correct explanation of (A). |
3. | (A) is true but (R) is false. |
4. | (A) is false but (R) is true. |
A wire of resistance R is connected in series with an inductor of reactance L. Then quality factor of RL circuit is
1.
2.
3.
4.
For a series LCR circuit, the power loss at resonance is
1.
2.
3.
4.
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 . The value of C is
1.
2.
3.
4.
A coil of inductive reactance 31 has a resistance of 8 . It is placed in series with a condenser of capacity reactance 25 . The combination is connected to an AC source of 110 V. The power factor of the circuit is
1. 0.56
2. 0.64
3. 0.80
4. 0.33
What is the value of inductance L for which the current is maximum in a series LCR circuit with C = 10F and = 1000 ?
1. 1 mH
2. cannot be calculated unless R is known
3. 10 mH
4. 100 mH
The primary and secondary coils of a transformer have 5O and 1500 turns respectively. If the magnetic flux linked with the primary coils is given by = + 4t, where is in webers, t is time in second and is a constant, the output voltage across the secondary coil is
1. 120 V
2. 220 V
3. 30 V
4. 90 V
The power dissipated in an LCR series circuit connected to an A.C. source of emf is
1.
2.
3.
4.
In the given circuit the reading of voltmeter and are 300V each. The reading of the voltmeter and ammeter A are respectively
1. 100 V, 2.0 A
2. 150 V, 2.2 A
3. 220 V, 2.2 A
4. 220 V, 2.0 A
A 220 V input is supplied to a transformer. The output circuit draws a current of 2.0 A at 440 V. If the efficiency of the transformer is 80%, the current drawn by the primary windings of the transformer is
1. 5.0 A
2. 3.6 A
3. 2.8 A
4. 2.5 A
An ac voltage is applied to a resistance R and inductor L in series. If R and the inductive reactance are both equal to 3 , the phase difference between the applied voltage and the current in the circuit is
1. zero
2. /6
3. /4
4. /2
In an ac circuit an alternating voltage e = sin100t V is connected to capacitor of capacity 1 . rms value of the current in the circuit is
1. 20 mA
2. 10 mA
3. 100 mA
4. 200 mA
A coil has resistance 30 and inductive reactance 20 at 50 Hz frequency. If an ac source, of 200V, 100 Hz, is connected across the coil, the current in the coil will be
1. 2.0 A
2. 4.0 A
3. 8.0 A
4. A
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 /3. If C is removed from the circuit, the phase difference is again /3. The power factor of the circuit is
1.
2.
3. 1
4.
A small-signal voltage is applied across an ideal capacitor C
1. Current I(t) is in phase with voltage V(t)
2. current I(t) leads voltage V(t) by 180
3. current I(t) lags voltage V(t) by 90
4. Over a full cycle, the capacitor C does not consume any energy from the voltage source.
Which of the following combinations should be selected for better tuning of an LCR circuit used for communication?
1. R = 25 , L = 2.5 h, C = 45
2. R = 15 , L = 3.5 h, C = 30
3. R = 25 , L = 1.5 h, C = 45
4. R = 20 , L = 1.5 h, C = 35