# Signals and Systems 3

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

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

Q2. Which of following is recursive system?

a) y(n – 1)

b) y(n + 1)

c) y(n)

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

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)

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)

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

a) Causal

b) Non-Causal

c) Depends on x(-n)

d) None

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

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

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

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°)

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

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)

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

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

Q14. Laplace transform of unit doublet is

a) 1/s

b) s2

c) s

d) None

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

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

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

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

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

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

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