# Electronics and Communication Engineering - Signals and Systems

### Exercise :: Signals and Systems - Section 1

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)

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%

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

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

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

Explanation:  .