Explore topic-wise MCQs in Electronics & Communication Engineering.

This section includes 1800 Mcqs, each offering curated multiple-choice questions to sharpen your Electronics & Communication Engineering knowledge and support exam preparation. Choose a topic below to get started.

101.

A capacitor whose capacitance Ct = C0 (1- cos ωt) is fed by a sinusoidal voltage v = V0 sin ωt. The equation for current i is

A. ω C0V0 cos ωt
B. ω C0V0 sin ωt
C. ω C0V0 (cos ωt - cos2 ωt)
D. none of the above
Answer» D. none of the above
Discussion
102.

The capacitance of a parallel plate capacitor varies as per the equation C(t) = C0 (1 - cos ωt). It is connected to a battery of V volts. The equation for current is

A. ωC0V (1 - cos ωt)
B. ωC0V(1 - sin ωt)
C. ωC0V (1 - sin 2ωt)
D. ωC0V sin ωt
Answer» E.
Discussion
103.

Two sinusoidal waves 1 and 2 have peak values Vm1 and Vm2. Wave 1 is leading wave 2 by ∠θ. Which of the following is correct?

A. v1 = Vm1 sin θ and v2 = Vm2 cos θ
B. v1 = Vm1 sin ωt and v2 = Vm2 sin (ωt - θ)
C. v1 = Vm1 sin (ωt + θ/2) and v2 = Vm2 sin ωt
D. none of the above
Answer» C. v1 = Vm1 sin (ωt + θ/2) and v2 = Vm2 sin ωt
Discussion
104.

In the set of equationx1 =

A. [A].
B. [B].
C. [C].
D. [D].
Answer» B. [B].
Discussion
105.

The resistance of a bulb at the time of full brightness is 1200 Ω. Then the resistance at room temperature is about

A. 1200 Ω
B. 120 Ω
C. 600 Ω
D. 10 Ω
Answer» C. 600 Ω
Discussion
106.

The power dissipated in 4 Ω resistance in figure is

A. 64 W
B. 32 W
C. 16 W
D. 8 W
Answer» D. 8 W
Discussion
107.

The frame of an electric motor is earthed through three earthing plates resistances 30 Ω, 20 Ω and 10 Ω respectively. During fault the energy dissipated by three plates are W1, W2 and W3. Then

A. W1 > W2 > W3
B. W1 < W2 < W3
C. W1 = W2 = W3
D. W1 + W3 < W2
Answer» C. W1 = W2 = W3
Discussion
108.

A series R-L circuit has R = 1 &ohm; and L = 1 H. It is excited by a V battery at t = 0. The steady state condition is reached at

A. t = 1 s
B. t = 0.1 s
C. t = 0 s
D. t = ∞
Answer» E.
Discussion
109.

An ac voltage 20 sin 1000t feeds an R-C series circuit. R = 8 &ohm; and active power is 4 W. The power factor is

A. 1
B. 0.8
C. 0.6
D. 0.4
Answer» E.
Discussion
110.

An R-L series circuit has R = 5 &ohm; and L = .01 H. It is fed by ac 50 Hz supply. The rms current in the circuit is 5 A. The active power supplied by the source is

A. 25 W
B. 50 W
C. 125 W
D. 250 W
Answer» D. 250 W
Discussion
111.

A series RLC circuit is supplied from a variable frequency source. The resonant frequency is ω0. The voltage across L is maximum at a frequency

A. equal to ω0
B. slightly less than ω0
C. slightly more than ω0
D. none of the above
Answer» D. none of the above
Discussion
112.

A series RLC circuit is supplied from a variable frequency ac source. The resonant frequency is ω0. The voltage across C is maximum at a frequency

A. equal to ω0
B. slightly less than ω0
C. slightly more than ω0
D. none of the above
Answer» C. slightly more than ω0
Discussion
113.

A series RC circuit has R = 5 &ohm; and C = 10 μF. The current in the circuit is 5 sin 20000t. The applied voltage is

A. 252 sin (20000t + 45°)
B. 252 sin (20000t - 45°)
C. 252 sin 20000t
D. 252 sin (20000t - 90°)
Answer» C. 252 sin 20000t
Discussion
114.

The circuit in figure, the switched on at t = 0. After a long time the current through 5 &ohm; resistance is

A. 1 A
B. 4 A
C. 10 A
D. 0
Answer» E.
Discussion
115.

A series RL circuit has . If a voltage 4 sint + 4t is applied, the steady state current will be

A. 4 sin (4t - 45°)
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
116.

In a one port network . It is excited by a unit step current. The initial and final values of voltage across the network impedance are

A. [A].
B. [B].
C. [C].
D. 1 and 0
Answer» B. [B].
Discussion
117.

A series circuit having R = 3 &ohm; and L = 2 H is excited by a 10 V battery. At t = 0+, di/dt is

A. 5 A/s
B. [B].
C. 20 A/s
D. 15 A/s
Answer» B. [B].
Discussion
118.

A series R, L, C circuit has R = 2&ohm;, L = 1H, C = 1 μF. It is connected to an ac variable frequency source of peak voltage 10 V. At resonance the power supplied by the source will be

A. 50 &ohm;
B. 25 &ohm;
C. 12.5 &ohm;
D. 6.25 &ohm;
Answer» C. 12.5 &ohm;
Discussion
119.

A series circuit has R = 5 &ohm; and C = 10 μF. At t = 0 it is switched on to a 10 V dc battery. The maximum current in the circuit is

A. 2 A
B. 1 A
C. 106A
D. 10 μA
Answer» B. 1 A
Discussion
120.

A series circuit has R = 5 &ohm; and C = 10 μF. It is switched on to a 12 V dc battery at t = 0. The current in the circuit will be maximum

A. at t = RC
B. at t = ∞
C. at t = 0+
D. none of the above
Answer» D. none of the above
Discussion
121.

A dc network has an open circuit voltage of 5 V. When its terminals are short circuited a current of 5 A flows through the short circuit. If the short circuit is removed and a resistance of 1.5 &ohm; is connected across its terminals, the current will be

A. 1 A
B. 2 A
C. 2.5 A
D. 5 A
Answer» C. 2.5 A
Discussion
122.

An RLC series circuit has . If the poles p1 and p1* are close to jω axis, then

A. Q is high
B. Q is low
C. ω0 is high
D. bandwidth is large
Answer» E.
Discussion
123.

The phase difference (jω - p1 )

A. phasor directed from p1 to jω
B. phasor directed from origin to p1
C. phasor directed from origin to jω point
D. phasor directed from jω to p1
Answer» B. phasor directed from origin to p1
Discussion
124.

A constant k high pass p section has a characteristic impedance of 300 &ohm; at f = ∞ . At f = fc, the characteristic impedance will be

A. zero
B. ∞
C. 300 &ohm;
D. more than 300 &ohm;
Answer» C. 300 &ohm;
Discussion
125.

Three impedances (3 + j 4) &ohm; each are connected in star. The impedances of equivalent delta circuit will be

A. 3 - j 4 &ohm; each
B. 9 + j 12 &ohm; each
C. 9 - j 12 &ohm; each
D. 3 + j 4, 3 - j 4 and 4 - j 3 &ohm;
Answer» C. 9 - j 12 &ohm; each
Discussion
126.

The internal impedance of a source is 3 + j 4 &ohm;. It is desired to supply maximum power to a resistive load. The load resistance should be

A. 3 &ohm;
B. 4 &ohm;
C. 7 &ohm;
D. 5 &ohm;
Answer» E.
Discussion
127.

The internal impedance of a source is 3 + j 7 &ohm;. For maximum power transfer, load impedance should be

A. 3 + j 7 &ohm;
B. 3 - j 7 &ohm;
C. 7 + j 3 &ohm;
D. 7 - j 3 &ohm;
Answer» C. 7 + j 3 &ohm;
Discussion
128.

An RLC series circuit has R = 7.07 &ohm;, L = .707 H and C = 7.07 μF. At Half power frequencies the circuit impedance is likely to be

A. 7.07 &ohm;
B. 10 &ohm;
C. 14.14 &ohm;
D. 20 &ohm;
Answer» C. 14.14 &ohm;
Discussion
129.

An RLC series circuit has Q = 100 and ω0 = 20 rad/sec. The bandwidth is

A. 0.2 rad/sec
B. 2 rad/sec
C. 20 rad/sec
D. 2000 rad/sec
Answer» B. 2 rad/sec
Discussion
130.

A two branch parallel circuit has a 10 &ohm; resistance and 0.5 H inductance in one branch and a 100 μF capacitor in the second branch. It is fed from 100 V ac supply. At resonance, the source current is

A. 10 A
B. 1 A
C. 0.2 A
D. 0.05 A
Answer» D. 0.05 A
Discussion
131.

A two branch parallel circuit has a 20 &ohm; resistance and 1 H inductance in one branch and a 100 μF capacitor in the second branch. It is fed from 100 V ac supply, at resonance, the input impedance of the circuit is

A. 500 &ohm;
B. 50 &ohm;
C. 20 &ohm;
D. 5 &ohm;
Answer» B. 50 &ohm;
Discussion
132.

An inductance having XL = 5 &ohm; and a capacitance having XC = 5 &ohm; are connected in parallel across 100 V, 50 Hz supply. The current drawn from source is

A. zero
B. 20 A
C. 40 A
D. 28.28 A
Answer» B. 20 A
Discussion
133.

Two sinusoidal voltage sources v1 = 50 sin (100t) and v1 = 50 sin (100t + p) are connected in parallel and fed an inductance XL = 2&ohm;. The cuirent through XL is

A. 25 A
B. about 17.5 A
C. zero
D. 50 A
Answer» D. 50 A
Discussion
134.

In an RC series circuit R = 100 &ohm; and XC = 10 &ohm;. In this circuit

A. the current and voltage are in phase
B. the current leads the voltage by about 6°
C. the current leads the voltage by about 84°
D. the current lags the voltage by about 6°
Answer» C. the current leads the voltage by about 84°
Discussion
135.

An RC series circuit has R = 20 &ohm; and XC = 20 &ohm;. Then Z =

A. 40 &ohm;
B. 28.28 &ohm;
C. 20 &ohm;
D. 1 &ohm;
Answer» C. 20 &ohm;
Discussion
136.

The impedance of an RC series circuit is 12 &ohm; at f= 50 Hz. At f= 200 Hz, the impedance will be

A. more than 12
B. less than 3
C. more than 3 &ohm; but less than 12 &ohm;
D. more than 12 &ohm; but less than 24 &ohm;
Answer» D. more than 12 &ohm; but less than 24 &ohm;
Discussion
137.

An RL series circuit has an impedance of 20 &ohm; when frequency is 25 Hz. At f= 50 Hz, the impedance will be

A. 40 &ohm;
B. 20 &ohm;
C. less than 40 W but more than 20 &ohm;
D. less than 20 W but more than 10 &ohm;
Answer» D. less than 20 W but more than 10 &ohm;
Discussion
138.

An RLC series circuit has R = 8 &ohm;, XL = 8 &ohm; and XC = 8 &ohm; Its impedance is

A. 8 + j 16 &ohm;
B. 8 + j 8 &ohm;
C. 8 &ohm;
D. 24 &ohm;
Answer» D. 24 &ohm;
Discussion
139.

If A = 16 ∠64°, (A)0.5 is

A. 4∠64°
B. 4∠8°
C. 4∠128°
D. 4∠32°
Answer» E.
Discussion
140.

If A = 4∠7°, A2 is

A. 16∠14°
B. 16∠49°
C. 16∠7°
D. 16∠3.5
Answer» B. 16∠49°
Discussion
141.

In the circuit of figure the current through 3 &ohm; resistance at t = ∞ is

A. 4 A
B. 2.5 A
C. 3.1 A
D. 0
Answer» C. 3.1 A
Discussion
142.

In the circuit of figure the current through 3 &ohm; resistance at t = 0+ is

A. 4 A
B. 2.5 A
C. 3.1 A
D. 0
Answer» E.
Discussion
143.

In the circuit of figure the current through 5 &ohm; resistance at t = ∞ is

A. 0 A
B. 10 A
C. 6.67 A
D. 5.1 A
Answer» B. 10 A
Discussion
144.

In the circuit of figure the current through L at t = ∞ is

A. 0 A
B. 10 A
C. 6.67 A
D. 5.1 A
Answer» C. 6.67 A
Discussion
145.

In the circuit of figure the current through 5 &ohm; resistance at t = 0+ is

A. 0 A
B. 10 A
C. 6.67 A
D. 5.1 A
Answer» D. 5.1 A
Discussion
146.

A series RL circuit is excited by a voltage v(t) = Ve-at such that a = R/L. Then the circuit current is

A. [A].
B. [B].
C. [C].
D. [D].
Answer» C. [C].
Discussion
147.

As B is increased from zero to about 2T, μr, of a ferromagnetic material

A. increase
B. decrease
C. first increases then decreases
D. remains the same
Answer» D. remains the same
Discussion
148.

The relative permeability of an iron specimen is 400 when B = 0.2 T. If B = 0.4 T, μr will be

A. 400
B. less than 400
C. more than 400
D. more or less than 400
Answer» E.
Discussion
149.

To find current in a resistance connected in a network, Thevenin's theorem is used VTH = 20 V and RTH = 5 &ohm;. The current through the resistance

A. is 4 A
B. is 4 A or less
C. is less than 4 A
D. may be 4 A or less or more than 4 A
Answer» D. may be 4 A or less or more than 4 A
Discussion
150.

In the circuit of figure, Thevenin's resistance is 10 &ohm;

A. 25 &ohm;
B. 10 &ohm;
C. 13.33 &ohm;
D. 6 &ohm;
Answer» C. 13.33 &ohm;
Discussion