Electronic Engineering MCQ Question Papers: ENTC, IT Interview Placement

Subject: Signals and Systems 3

**Part 3: List for questions and answers of Signals and Systems**

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**Q1. An ac circuit has an impedance of (3 + j6) ohm for fundamental. The impedance for fifth ****harmonic is**

**a) (15 + j 30) O**

**b) (15 + j 6) O**

**c) (3 + j 30) O**

**d) (3 + j 1.2) O**

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**Q2. Which of following is recursive system?**

**a) y(n – 1)**

**b) y(n + 1)**

**c) y(n)**

**d) y(n) + y(n + 1)**

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**Q3. In terms of sine function sin (t), unit step function u(t) =**

**a) 1 + sin(t)**

**b) 1 – sin (t)**

**c) 0.5 + 0.5 sin (t)**

**d) 0.5 – 0.5 sin (t)**

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**Q4. Choose correct option**

**a) Var (X + Y) = Var (X) + Var (Y)**

**b) Var (X – Y) = Var (X) + Var (Y)**

**c) Var (X + Y) = Var (X) x Var (Y)**

**d) Both (a) and (b)**

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**Q5. If sequence y(n) = x(-n) then it is**

**a) Causal**

**b) Non-Causal**

**c) Depends on x(-n)**

**d) None**

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**Q6. An ac network has a power factor of 0.8 lagging for fundamental frequency. If the ****applied voltage contains third and fifth harmonics, the overall power factor will be**

**a) More than 0.8 lagging**

**b) 0.8 lagging**

**c) Less than 0.8 lagging**

**d) 0.8 lagging or less **

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**Q7. If a function has only cosine terms, it must satisfy the equation**

**a) f(t) = -f(t)**

**b) f(-t) = f(t)**

**c) f(-t) = -f(t)**

**d) None of the above**

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**Q8. A 1 kHz sinusoidal signal is ideally sampled at 1500 samples/sec and the sampled signal ****is passed through an ideal low pass filter with cut off frequency 800 Hz. The output signal ****has the frequency**

**a) 0 Hz**

**b) 0.75 kHz**

**c) 0.5 kHz**

**d) 0.25 kHz**

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**Q9. If i = 10 + 12 cos 500t – 3.5 sin 500 t, then in amplitude phase form i =**

**a) 10 + 12.5 sin (500 t + 106.20°)**

**b) 5 + 12.5 sin (500 t + 106.20°)**

**c) 10 + 11 sin (500 t + 106.20°)**

**d) 10 + 12.5 sin (500 t + 10°)**

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**Q10. A pulse function having magnitude E and duration from t = 0 to t = a can be ****represented as**

**a) Sum of two pulse functions**

**b) Difference of two pulse functions**

**c) Difference of two step functions each of magnitude E and one originating at t = 0 and**

**the other at t = a**

**d) None of the above**

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**Q11. A rectangular pulse is passed through an L.P.F. The response is a**

**a) Triangular**

**b) Trapezoidal function**

**c) Sampling**

**d) Both (a) and (b)**

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**Q12. A signal f(t) = cos 10wt + 3 cos 4wt is instantaneously sampled. The maximum ****allowable value of sampling interval Ts in sec is**

**a) 1 / 4 sec**

**b) 1 / 8 sec**

**c) 1 / 8p sec**

**d) 1 / 10 sec **

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**Q13. Principle of superposition is applicable to**

**a) Linear systems only**

**b) Nonlinear systems only**

**c) Both linear and non linear system**

**d) Linear systems and some nonlinear systems**

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**Q14. Laplace transform of unit doublet is**

**a) 1/s**

**b) s2**

**c) s**

**d) None**

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**Q15. The integral of a unit step function is**

**a) A unit impulse function**

**b) A unit pulse function**

**c) A ramp function of slope 1**

**d) None of the above**

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**Q16. A voltage wave containing 10% third harmonic is applied to a scries R-L circuit. The ****percentage third harmonic content in the current wave will be**

**a) More than 10%**

**b) 10% or less than 10%**

**c) Less than 10%**

**d) 10% or more or less**

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**Q17. Two rectangular waveforms of duration t1 and t2 seconds are convolved. What is the ****shape of the resulting waveform?**

**a) Triangular**

**b) Rectangular**

**c) Trapezoidal**

**d) Semi-circular**

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**Q18. Auto correlation for (t)= 0 is equal to**

**a) Average power S of waveform**

**b) Square of average power S of waveform**

**c) Half of average power S of waveform**

**d) Square root of average power S of waveform **

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**Q19. For an ac sinusoidal wave, the rms value is 10 A. For the same wave delayed by 60° in ****each half cycle, the rms value is likely to be**

**a) 10 A**

**b) 7.07 A**

**c) 6.35 A**

**d) 3.5 A**

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**Q20. Which one of the following is the correct statement of the system characterized by the ****equation y(t) = ax(t) + b?**

**a) Linear for any value of b**

**b) Linear if b is greater than 0**

**c) Linear if b is less than 0**

**d) Non-linear **

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**Part 3: List for questions and answers of Signals and Systems**

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**Q1. Answer: c**

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**Q2. Answer: a**

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**Q3. Answer: c**

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**Q4. Answer: d**

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**Q5. Answer: c**

**Q6. Answer: c**

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**Q7. Answer: b**

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**Q8. Answer: c**

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**Q9. Answer: a**

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**Q10. Answer: c**

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**Q11. Answer: a**

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**Q12. Answer: d**

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**Q13. Answer: a**

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**Q14. Answer: c**

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**Q15. Answer: c**

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**Q16. Answer: c**

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**Q17. Answer: c**

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**Q18. Answer: a**

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**Q19. Answer: a**

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**Q20. Answer: d**