GATE EC ||SIGNALS AND SYSTEMS ||FOURIER SERIES & FOURIER TRANSFORM || PYQs

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Question 1

One period (0, T) each of two periodic waveforms W1 and W2 are shown in the figure. The magnitudes of the nth Fourier series coefficients of W1 and W2, for n ≥ 1, n is odd, are respectively proportional to

Screenshot-2025-09-08-155325

(GATE 2000 || EC || PYQ || MCQ || 2 MARKS)

  • |n|–3 and |n|–2

  •  |n|–2 and |n|–3

  •  |n|–1 and |n|–2

  • |n|–4 and |n|–2

Question 2

A periodic g(t) is shown in figure. Determine the PSD of g(t).

Screenshot-2025-09-08-155707


(GATE 2001 || EC || PYQ || NAT || 5 MARKS)

  • ans

    Screenshot-2025-09-08-155756


Question 3

Which of the following cannot be the Fourier series expansion of a periodic signal?

(GATE 2001 || EC || PYQ || MCQ || 1 MARKS)

  • x(t) = 2cost + 3cos3t

  • x(t) = 2cosπt + 7cost

  •  x(t) = cost + 0.5

  • x(t) = 2cos1.5πt + sin 3.5πt

Question 4

The Fourier series expansion of a real periodic signal with fundamental frequency f0 is given by:

[Tex]g_p(t) = \sum_{n=-\infty}^{\infty} C_n e^{j2\pi n f_0 t}[/Tex]

It is given that C3 = 3 + j5. Then C–3 is

(GATE 2003 || EC || PYQ || MCQ || 1 MARKS)

  • 5 + j3

  • -3- j5

  • -5 + j3

  • 3 - j5

Question 5

Choose the function f(t), –∞< t <∞, for which a Fourier series cannot be defined?

(GATE 2005 || EC || PYQ || MCQ || 1 MARKS)

  • 3sin (25t)

  • 4 cos (20t + 3) + 2sin(10t)

  •  exp (–|t|) sin (25t)

  • 1

Question 6

A function is given by f(t) = sin2t + cos 2t. Which of the following is true?


(GATE 2009 || EC || PYQ || MCQ || 1 MARKS)

  • Screenshot-2025-09-08-161625


  • Screenshot-2025-09-08-161630


  • Screenshot-2025-09-08-161635


  • Screenshot-2025-09-08-161646


Question 7

The Fourier series of a real periodic function has only

  • P. Cosine terms if it is even
  • Q. Sine terms if it is even
  • R. Cosine terms if it is odd
  • S. Sine terms if it is odd

Which of the above statements are correct?

(GATE 2009 || EC || PYQ || MCQ || 1 MARKS)

  • P and S

  •  P and R

  •  Q and S

  •  Q and S

Question 8

The trigonometric Fourier series for the waveform f(t) shown below contains

Screenshot-2025-09-08-162334

(GATE 2010 || EC || PYQ || MCQ || 1 MARKS)

  •  Only cosine terms and zero value for the dc component

  • Only cosine terms and a positive value for the dc component

  • Only cosine terms and a negative value for the dc component

  • Only sine terms and a negative for the dc component

Question 9

The trigonometric Fourier series of an even function does not have the:

(GATE 2011 || EC || PYQ || MCQ || 1 MARKS)

  • dc term

  •  cosine terms

  • sine terms

  • odd harmonic terms

Question 10

Consider the periodic square wave in the figure shown.

Screenshot-2025-09-08-163248

The ratio of the power in the 7th harmonic to the power in the 5th harmonic for this waveform is closest in value to _____.


(GATE 2014 || EC || PYQ || NAT || 1 MARKS)

  • 0.5

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