# Questions & Answers of Electric Circuits and Fields

#### Topics of Electric Circuits and Fields 100 Question(s) | Weightage 16 (Marks)

Question No. 25

RA and RB are the input resistances of circuits as shown below. The circuits extend infinitely in the direction shown. Which one of the following statements is TRUE?

Question No. 27

In the portion of a circuit shown, if the heat generated in 5 Ω resistance is 10 calories per second, then heat generated by the 4 Ω resistance, in calories per second, is _______.

Question No. 35

If an ideal transformer has an inductive load element at port 2 as shown in the figure below, the equivalent inductance at port 1 is

Question No. 49

In the circuit shown, switch S2 has been closed for a long time. At time t=0 switch S1 is closed. At t=0+, the rate of change of current through the inductor, in amperes per second, is _____.

Question No. 62

In the circuit shown below, the supply voltage is $10\mathrm{sin}\left(1000t\right)$ volts. The peak value of the steady state current through the 1 Ω resistor, in amperes,

Question No. 63

A dc voltage with ripple is given by $v\left(t\right)=\left[100+10\mathrm{sin}\left(\omega t\right)-5\mathrm{sin}\left(3\omega t\right)\right]$ volts. Measurements of this voltage $v\left(t\right)$, made by moving-coil and moving-iron voltmeters, show readings of V1 and V2 respectively. The value of V2V1, in volts, is _________.

Question No. 64

The circuit below is excited by a sinusoidal source. The value of R, in Ω, for which the admittance of the circuit becomes a pure conductance at all frequencies is _____________.

Question No. 65

In the circuit shown below, the node voltage VA is ___________ V.

Question No. 113

The following figure shows the connection of an ideal transformer with primary to secondary turns ratio of 1:100. The applied primary voltage is 100 V (rms), 50 Hz, AC. The rms value of the current I, in ampere, is __________.

Question No. 121

A resistance and a coil are connected in series and supplied from a single phase, 100 V, 50 Hz ac source as shown in the figure below. The rms values of plausible voltages across the resistance (VR) and coil (VC) respectively, in volts, are

Question No. 122

The voltage (V) and current (A) across a load are as follows.

$v\left(t\right)=100\mathrm{sin}\left(\omega t\right)$ ,

The average power consumed by the load, in W, is___________.

Question No. 133

In the circuit shown below, the voltage and current sources are ideal. The voltage (Vout) across the current source, in volts, is

Question No. 134

The graph associated with an electrical network has 7 branches and 5 nodes. The number of independent KCL equations and the number of independent KVL equations, respectively, are

Question No. 144

The driving point input impedance seen from the source Vs of the circuit shown below, in Ω, is ______.

Question No. 145

The z-parameters of the two port network shown in the figure are . The average power delivered to ${R}_{L}=20\Omega$ , in watts, is _______.

Question No. 146

In the balanced 3-phase, 50 Hz, circuit shown below, the value of inductance (L) is 10 mH. The value of the capacitance (C) for which all the line currents are zero, in millifarads, is ___________.

Question No. 147

In the circuit shown below, the initial capacitor voltage is 4 V. Switch S1 is closed at $t=0$. The charge (in μC) lost by the capacitor from t = 25 μs to t = 100 μs is ____________.

Question No. 28

The voltages developed across the 3 Ω and 2 Ω resistors shown in the figure are 6V and 2V respectively, with the polarity as marked. What is the power (in Watt) delivered by the 5V voltage source?

Question No. 29

For the given circuit the Thevenin equivalent is to be determined. The Thevenin voltage,${V}_{Th}$(in volt), seen from terminal AB is _________.

Question No. 30

An inductor is connected in parallel with a capacitor as shown in the figure.

As the frequency of current i is increased, the impedance (Z) of the network varies as

Question No. 32

The self inductance of the primary winding of a single phase, 50 Hz, transformer is 800 mH, and that of the secondary winding is 600 mH. The mutual inductance between these two windings is 480 mH. The secondary winding of this transformer is short circuited and the primary winding is connected to a 50 Hz, single phase, sinusoidal voltage source. The current flowing in both the winding is less than their respective rated currents. The resistance of both windings can be neglected. In this connection, what is the effective inductance (in mH) seen by the source?

Question No. 55

The circuit shown in the figure has two sources connected in series. The instantaneous voltage of the AC source (in volt) is given by v(t) = 12 sint. If the circuit is in steady-state, then the rms value of the current (in Ampere) flowing in the circuit is ______.

Question No. 56

In a linear two-port network, when 10 V is applied to Port 1, a current of 4 A flows through Port 2 when it is short-circuited. When 5 V is applied to Port1, a current of 1.25 A flows through a 1$\mathrm{\Omega }$ resistance connected across Port 2. When 3 V is applied to Port 1, then current (in Ampere) through a 2$\mathrm{\Omega }$ resistance connected across Port 2 is _________.

Question No. 57

In the given circuit, the parameter k is positive, and the power dissipated in the 2$\mathrm{\Omega }$ resistor is 12.5 W. The value of k is________.

Question No. 128

A series RL circuit is excited at t = 0 by closing a switch as shown in the figure. Assuming zero initial conditions, the value of $\frac{{\mathrm{d}}^{2}i}{\mathrm{d}{t}^{2}}$ at t = ${0}^{+}$ is

Question No. 129

The current i (in Ampere) in the 2 $\mathrm{\Omega }$ resistor of the given network is ____ .

Question No. 130

Find the transformer ratios a and b that the impedance (${\mathrm{Z}}_{in}$) is resistive and equal 2.5$\mathrm{\Omega }$ when the network is excited with a sine wave voltage of angular frequency of 5000 rad/s.

Question No. 154

In the given network ${V}_{1}=100\angle {0}^{°}$0°V, ${V}_{2}=100\angle -{120}^{°}$V, ${V}_{3}=100\angle +{120}^{°}$V. The phasor current i (in Ampere) is

Question No. 156

Two identical coils each having inductance L are placed together on the same core. If an overall inductance of $\alpha$L is obtained by interconnecting these two coils, the minimum value of $\alpha$ is ________.

Question No. 16

The three circuit elements shown in the figure are part of an electric circuit. The total power absorbed by the three circuit elements in watts is __________.

Question No. 17

C0 is the capacitance of a parallel plate capacitor with air as dielectric (as in figure (a)). If, half of the entire gap as shown in figure (b) is filled with a dielectric of permittivity ${\mathit{\in }}_{r}$, the expression for the modified capacitance is

Question No. 18

A combination of 1 µF capacitor with an initial voltage${\nu }_{c}\left(0\right)=-2\nu$ in series with a 100 O resistor is connected to a 20 mA ideal dc current source by operating both switches at t = 0 s as shown. Which of the following graphs shown in the options approximates the voltage vs across the current source over the next few seconds?

Question No. 39

An incandescent lamp is marked 40 W, 240V. If resistance at room temperature (26°C) is 120 Ω, and temperature coefficient of resistance is 4.5x10-3/°C, then its ‘ON’ state filament temperature in °C is approximately _______

Question No. 40

In the figure, the value of resistor R is (25 + I/2) ohms, where I is the current in amperes. The current I is ______

Question No. 42

The following four vector fields are given in Cartesian co-ordinate system. The vector field which does not satisfy the property of magnetic flux density is

Question No. 116

Two identical coupled inductors are connected in series. The measured inductances for the two possible series connections are 380 μH and 240 μH. Their mutual inductance in μH is ________

Question No. 117

The switch SW shown in the circuit is kept at position ‘1’ for a long duration. At t = 0+, the switch is moved to position ‘2’. Assuming |Vo2| > |Vo1|, the voltage vc(t) across the capacitor is

Question No. 118

A parallel plate capacitor consisting two dielectric materials is shown in the figure. The middle dielectric slab is placed symmetrically with respect to the plates.

If the potential difference between one of the plates and the nearest surface of dielectric interface is 2 Volts, then the ratio ε1 : ε2 is

Question No. 121

Assuming an ideal transformer, the Thevenin’s equivalent voltage and impedance as seen from the terminals x and y for the circuit in figure are

Question No. 140

The voltage across the capacitor, as shown in the figure, is expressed as

${V}_{c}\left(t\right)={A}_{1}\mathrm{sin}\left({\omega }_{1}t-{\theta }_{1}\right)+{A}_{2}\mathrm{sin}\left({\omega }_{2}t-{\theta }_{2}\right)$

The values of  A 1and  A 2 respectively, are

Question No. 141

The total power dissipated in the circuit, shown in the figure, is 1 kW.

The voltmeter, across the load, reads 200 V. The value of  XL is ___________.

Question No. 142

The magnitude of magnetic flux density $\left(\overrightarrow B\right)$ at a point having normal distanced meters from an infinitely extended wire carrying current of I A is$\frac{{\mu }_{0}I}{2\pi d}$ (in SI units). An infinitely extended wire is laid along the x-axis and is carrying current of 4 A in the +ve x direction. Another infinitely extended wire is laid along the y-axis and is carrying 2 A current in the +ve y direction. ${\mu }_{0}$ is permeability of free space. Assume $\widehat i$, $\widehat j$, $\widehat k$ to be unit vectors along x, y and z axes respectively

Assuming right handed coordinate system, magnetic field intensity, $\overrightarrow H$ at coordinate (2,1,0) will be

Question No. 216

The line A to neutral voltage is A1015oV for a balanced three phase star-connected load with phase sequence ABC. The voltage of line B with respect to line C is given by

Question No. 218

The driving point impedance Z(s) for the circuit shown below is

Question No. 234

A non-ideal voltage source Vs has an internal impedance of Zs. If a purely resistive load is to be chosen that maximizes the power transferred to the load, its value must be

Question No. 239

The Norton’s equivalent source in amperes as seen into the terminals X and Y is _______.

Question No. 240

The power delivered by the current source, in the figure, is ________.

Question No. 242

A series RLC circuit is observed at two frequencies. At ω1=1 krad/s, we note that source voltage ${V}_{1}=100\angle {0}^{o}V$ results in a current ${I}_{1}=0.03\angle {31}^{o}A$. At ${\omega }_{2}=2$ krad/s, the source voltage ${V}_{2}=100\angle {0}^{o}V$ results in a current ${I}_{1}=2\angle {31}^{o}A$. The closest values for R,L,C out of the following options are

Question No. 7

A source ${\nu }_{s}\left(t\right)=V\mathrm{cos}100\pi t$ has an internal impedance of $\left(4+j3\right)\mathrm{\Omega }$.If a purely resistive load connected to this source has to extract the maximum power out of the source, its value in $\mathrm{\Omega }$ should be

Question No. 10

The flux density at a point in space is given by $\mathbf{B}\mathbf{=}4x{\mathbf{a}}_{\mathrm{x}}+2ky{\mathbf{a}}_{\mathbf{y}}+8{\mathbf{a}}_{\mathbf{z}}$ Wb/m2. The value of constant k must be equal to

Question No. 19

Consider a delta connection of resistors and its equivalent star connection as shown below. If all elements of the delta connection are scaled by a factor k, k > 0, the elements of the corresponding star equivalent will be scaled by a factor of

Question No. 29

In the circuit shown below, if the source voltage ${V}_{s}=100\angle 53.13°\mathrm{V}$ then Thevenin’s equivalent voltage in Volts as seen by the load resistance RL is

Question No. 30

Three capacitors C1, C2, and C3, whose values are 10μF, 5μF, and 2μF respectively, have breakdown voltages of 10V, 5V, and 2V respectively. For the interconnection shown, the maximum safe voltage in Volts that can be applied across the combination and the corresponding total charge in μC stored in the effective capacitance across the terminals are respectively

Question No. 42

Two magnetically uncoupled inductive coils have Q factors q1 and q2 at the chosen operating frequency. Their respective resistances are R1 and R2. When connected in series, their effective Q factor at the same operating frequency is

Question No. 43

The following arrangement consists of an ideal transformer and an attenuator which attenuates by a factor of 0.8. An ac voltage VWX1 = 100V is applied across WX to get an open circuit voltage VYZ1  across YZ. Next, an ac voltage VYZ2  = 100V is applied across YZ to get an open circuit voltage VWX2  across WX. Then, VYZ1/VWX1,VWX2/VYZ2 are respectively,

Question No. 4

In the circuit shown below, the current through the inductor is

Question No. 5

The impedance looking into nodes 1 and 2 in the given circuit is

Question No. 11

A two-phase load draws the following phase currents: ${i}_{1}\left(t\right)={I}_{m}\mathrm{sin}\left(\omega t-{\Phi }_{1}\right)$, ${i}_{2}\left(t\right)={I}_{m}\mathrm{cos}\left(\omega t-{\Phi }_{2}\right)$.These currents are balanced if ${\Phi }_{1}$ is equal to

Question No. 16

The average power delivered to an impedance (4-j3)$\Omega$ by a current $5\mathrm{cos}\left(100\pi t+100\right)A$ is

Question No. 17

In the following figure, C1 and C2 are ideal capacitors. C1 has been charged to 12 V before the ideal switch S is closed at t = 0. The current i(t) for all t is

Question No. 28

If VA-VB=6V, then VC-VD is

Question No. 40

Assuming both the voltage sources are in phase, the value of R for which maximum power is transferred from circuit A to circuit B is

Question No. 50

With 10 V dc connected at port A in the linear nonreciprocal two-port network shown below, the following were observed:

(i) 1Ω connected at port B draws a current of 3 A
(ii) 2.5Ω connected at port B draws a current of 2 A

For the same network, with 6 V dc connected at port A, 1Ω connected at port B draws 7/3 A. If 8 V dc is connected to port A, the open circuit voltage at port B is

Question No. 51

With 10 V dc connected at port A in the linear nonreciprocal two-port network shown below, the following were observed:

(i) 1Ω connected at port B draws a current of 3 A
(ii) 2.5Ω connected at port B draws a current of 2 A

With 10 V dc connected at port A, the current drawn by 7Ω connected at port B is

Question No. 52

In the circuit shown, the three voltmeter readings are V1=220V , V2=122V , V3=136V .

The power factor of the load is

Question No. 53

In the circuit shown, the three voltmeter readings are V1=220V , V2=122V , V3=136V .

If RL=5Ω, the approximate power consumption in the load is

The voltage applied to a circuit is 100 $\sqrt{2}$ cos (100$\pi$t) volts and the circuit draws a current of 10 $\sqrt{2}$ sin (100$\pi$t + $\pi$ / 4) amperes. Taking the voltage as the reference phasor, the phasor representation of the current in amperes is