In a synchronous counter with n flip-flops, what is the maximum frequency at which the counter can operate?

The correct answer is B: f_max = 1/t_pd, where t_pd is the propagation delay of one flip-flop. In synchronous counters, all flip-flops are clocked simultaneously, so the maximum frequency is limited only by the propagation delay of a single flip-flop, not the cumulative delay.

A Zener diode is operating in reverse breakdown with a current of 50 mA. If the Zener resistance is 5 Ω and Zener voltage is 12 V, what is the terminal voltage?

The correct answer is A: 12.25 V. Terminal voltage = Vz + Iz·Rz = 12 + (50×10^-3 × 5) = 12 + 0.25 = 12.25 V

For maximum power transfer from a source with internal resistance Rs to load RL, what should be the condition?

The correct answer is B: RL = Rs (impedance matching). Maximum power transfer theorem states that maximum power is delivered when load impedance equals the complex conjugate of source impedance. For resistive cases, RL = Rs.

For a stable IIR filter with difference equation y[n] = 0.5y[n-1] + x[n], the DC gain is:

The correct answer is C: 2. DC gain = H(z=1) = 1/(1-0.5) = 1/0.5 = 2

In a p-n junction diode, the depletion region width depends on which of the following factors?

The correct answer is A: Applied voltage and doping concentrations. Depletion width W = √(2εV/qNd·Na/(Nd+Na)), dependent on applied voltage and doping concentrations.

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Electronics (ECE)

Analog/digital electronics, communication

135 Q 4 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 135

Topics in Electronics (ECE)

All Electronic Devices 100 Digital Electronics 100 Analog Circuits 100 Signals & Systems 100

Q.1 Easy Signals & Systems

A first-order low-pass filter has transfer function H(s) = ωc/(s + ωc). At what frequency (in terms of ωc) does the magnitude response drop to 1/√2 of its DC value?

A ω = ωc/2

B ω = ωc

C ω = 2ωc

D ω = ωc/√2

Correct Answer: B. ω = ωc

EXPLANATION

At DC (ω=0): |H(j0)| = 1. At ω = ωc: |H(jωc)| = ωc/√(ωc² + ωc²) = 1/√2. This is the -3dB cutoff frequency, a fundamental property of first-order filters.

Test

Q.2 Easy Signals & Systems

The Z-transform of a discrete-time signal is X(z) = z/(z-0.5) with ROC |z| > 0.5. The corresponding time-domain signal is:

A x[n] = 0.5^n × u[n]

B x[n] = δ[n] + 0.5^n × u[n]

C x[n] = 0.5^(n-1) × u[n-1]

D x[n] = δ[n-1] × 0.5^n

Correct Answer: A. x[n] = 0.5^n × u[n]

EXPLANATION

Using partial fractions or standard Z-transform tables: X(z) = z/(z-0.5) corresponds to x[n] = 0.5^n × u[n] where u[n] is the unit step function. The ROC |z| > 0.5 confirms a causal right-sided sequence.

Test

Q.3 Easy Signals & Systems

The energy of a signal x[n] = {1, 2, -1, 0} is:

A 4

B 6

C 5

D 3

Correct Answer: B. 6

EXPLANATION

Energy = 1² + 2² + (-1)² + 0² = 1 + 4 + 1 + 0 = 6.

Test

Q.4 Easy Signals & Systems

An even signal x(t) has Fourier transform X(f). What can be said about X(f)?

A X(f) is purely imaginary

B X(f) is real and even

C X(f) is complex

D X(f) is purely real but odd

Correct Answer: B. X(f) is real and even

EXPLANATION

For an even signal, the Fourier transform is real and even: X(-f) = X(f) and X*(f) = X(f).

Test

Q.5 Easy Signals & Systems

The Z-transform of x[n] = (1/2)^n u[n] is:

A z/(z - 0.5), |z| > 0.5

B 1/(1 - 0.5z^(-1)), |z| > 0.5

C z/(z - 2), |z| > 2

D 0.5z/(z - 1), |z| > 1

Correct Answer: A. z/(z - 0.5), |z| > 0.5

EXPLANATION

X(z) = Σ(1/2)^n z^(-n) = z/(z - 1/2) = z/(z - 0.5) with ROC |z| > 0.5.

Test

Q.6 Easy Signals & Systems

A causal LTI system has impulse response h(t) = e^(-3t)u(t). Is this system stable?

A Yes, because the impulse response is absolutely integrable

B No, because the pole is at s = 3

C No, because the ROC doesn't include the jω axis

D Yes, but only for t > 0

Correct Answer: A. Yes, because the impulse response is absolutely integrable

EXPLANATION

∫₀^∞ e^(-3t) dt = 1/3 < ∞. For stability, BIBO condition requires absolute integrability, which is satisfied.

Test

Q.7 Easy Signals & Systems

Which property of the Fourier transform states that multiplication in time domain equals convolution in frequency domain?

A Linearity

B Modulation theorem

C Parseval's theorem

D Time-shifting property

Correct Answer: B. Modulation theorem

EXPLANATION

The modulation theorem (or frequency convolution property) states that x(t)×y(t) ↔ X(f)*Y(f).

Test

Q.8 Easy Signals & Systems

A continuous-time signal x(t) = 5sin(100πt) is sampled at 150 Hz. What is the Nyquist frequency required to avoid aliasing?

A 50 Hz

B 100 Hz

C 150 Hz

D 200 Hz

Correct Answer: B. 100 Hz

EXPLANATION

The maximum frequency in the signal is 50 Hz (from 100π = 2πf). Nyquist frequency = 2 × 50 = 100 Hz.

Test

Q.9 Easy Signals & Systems

A system with transfer function H(s) = (s+2)/(s²+3s+2) has poles at:

A s = -1, -2

B s = 1, 2

C s = -1 ± j

D s = 2, -3

Correct Answer: A. s = -1, -2

EXPLANATION

Denominator s²+3s+2 = (s+1)(s+2) = 0, giving poles at s = -1 and s = -2.

Test

Q.10 Easy Signals & Systems

The convolution of two signals each of length 5 using linear convolution yields an output of length:

A 5

B 9

C 10

D 25

Correct Answer: B. 9

EXPLANATION

Linear convolution of signals of length M and N produces output of length M+N-1 = 5+5-1 = 9.

Test

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