Electronics and Communication Engineering - Signals and Systems

31. 

A signal m(t) is multiplied by a sinusoidal waveform of frequency fc such that
v(t)=m(t) cos 2pfct
If Fourier transform of m(t) is M(f), Fourier transform of v(t) will be

A. 0.5 M(f + fc)
B. 0.5 M(f - fc)
C. 0.5 M(f + fc) + 0.5 M(f - fc)
D. 0.5 M(f - fc) + 0.5 M(f - fc)

Answer: Option C

Explanation:

It is a modulation process. The resultant has (f + fc) and (f - fc) terms.


32. 

A voltage wave having 5% fifth harmonic content is applied to a series RC circuit. The percentage fifth harmonic content in the current wave will be

A. 5%
B. more than 5%
C. less than 5%
D. equal or more than 5%

Answer: Option B

Explanation:

IC = V(jωC).


33. 

Assertion (A): If , the initial value of i(t) is 5A

Reason (R): As per initial vaue theroem

A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is true, R is false
D. A is false, R is true

Answer: Option A

Explanation:

Initial value theorem when applied to I(s) gives 5 A.


34. 

δ(t) is a

A. energy signal
B. power signal
C. neither energy nor power
D. none

Answer: Option B

Explanation:

Because Unit step is a Power signal. So By trignometric identifies d(t) also power.

.


35. 

The analog signal given below is sampled by 600 samples per second for m(t) = 3 sin 500 pt + 2 sin 700 pt then folding frequency is

A. 500 Hz
B. 700 Hz
C. 300 Hz
D. 1400 Hz

Answer: Option C

Explanation:

.