1Which of the following represents the trigonometric Fourier series of a periodic function defined in the interval ?
A.
B.
C.
D.
Correct Answer:
Explanation:This is the standard general form of the Fourier series for a function with period . The term represents the average value (DC component).
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2For a function defined in , Euler's formula for the coefficient () is given by:
A.
B.
C.
D.
Correct Answer:
Explanation:The Fourier cosine coefficient is calculated by integrating the product of the function and over the period, normalized by .
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3For a function defined in , Euler's formula for the coefficient is given by:
A.
B.
C.
D.
Correct Answer:
Explanation:The Fourier sine coefficient is found by integrating over the interval, divided by the half-period .
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4If the Fourier series is expressed as , what is the formula for in the interval ?
A.
B.
C.
D.
Correct Answer:
Explanation:With the constant term defined as , . This ensures is the mean value of the function.
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5Which of the following is NOT one of Dirichlet's conditions for the existence of a Fourier series for ?
A. must be periodic, single-valued, and finite.
B. must have a finite number of discontinuities in any one period.
C. must be differentiable everywhere in the interval.
D. must have a finite number of maxima and minima in any one period.
Correct Answer: must be differentiable everywhere in the interval.
Explanation:Dirichlet's conditions do not require the function to be differentiable everywhere; it allows for points of finite discontinuity. The other options are required conditions.
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6If a function satisfies Dirichlet's conditions, at a point of finite discontinuity , the Fourier series converges to:
A.
B.
C.
D.
Correct Answer:
Explanation:At a point of discontinuity, the Fourier series converges to the arithmetic mean of the left-hand limit and the right-hand limit of the function at that point.
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7The value of the integral (where are integers) is:
A. if
B.$0$ for all integer
C. if
D.$1$
Correct Answer: $0$ for all integer
Explanation:The product of an odd function () and an even function () is an odd function. The integral of an odd function over a symmetric interval is always zero.
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8For an even function defined in , which Fourier coefficients are always zero?
A.
B.
C.
D.None of the coefficients
Correct Answer:
Explanation:For an even function, the Fourier series consists only of cosine terms (and the constant). Therefore, all sine coefficients are zero.
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9If is an odd function in , then is given by:
A.
B.
C.
D.
Correct Answer:
Explanation:For an odd function, the product is odd (Odd Even = Odd). The integral of an odd function over a symmetric interval is zero.
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10Which of the following functions is an Even function?
A.
B.
C.
D.
Correct Answer:
Explanation: satisfies , which is the definition of an even function. is Odd Even = Odd.
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11In the Fourier expansion of in , the value of is:
A.
B.
C.$0$
D.
Correct Answer: $0$
Explanation:The function is the sum of two odd functions, making odd. For any odd function in a symmetric interval, .
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12For a function defined in the interval , the coefficient is calculated as:
A.
B.
C.
D.
Correct Answer:
Explanation:For a general interval of length (period ), the formula uses the normalization factor and integrates over the full period .
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13What is the Fourier Series expansion of in the Half Range Cosine Series for ?
A.
B.
C.
D.
Correct Answer:
Explanation:A half range cosine series expands a function defined in by extending it as an even function to . This results in only cosine terms and a constant.
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14To expand as a Half Range Sine Series in , we extend the function to the interval as:
A.An even function
B.An odd function
C.A periodic function
D.A constant function
Correct Answer: An odd function
Explanation:To obtain only sine terms (which are odd), the function must be extended to the negative interval such that , creating an odd function.
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15The coefficient in a Half Range Sine Series for in is:
A.
B.
C.
D.
Correct Answer:
Explanation:For a half range series, we integrate over and multiply by (which comes from the even/odd property simplification of the standard integral over ).
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16Parseval's formula for a function with period in states that:
A.
B.
C.
D.
Correct Answer:
Explanation:This is the standard form of Parseval's identity relating the average power of the function to the sum of the squares of its Fourier coefficients.
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17In the Complex form of Fourier Series defined in , the coefficient is given by:
A.
B.
C.
D.
Correct Answer:
Explanation:The complex coefficient is derived using the orthogonality of exponentials. The normalization factor for the interval length is .
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18The relationship between the complex coefficient and the real coefficients (for ) is:
A.
B.
C.
D.
Correct Answer:
Explanation:Using Euler's identity on the real series, the term corresponds to .
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19For a real-valued function , the complex coefficients satisfy the property:
A. (Complex Conjugate)
B.
C.
D.
Correct Answer: (Complex Conjugate)
Explanation:For real-valued signals, the spectrum is Hermitian symmetric, meaning the coefficient for negative frequency is the complex conjugate of the positive frequency.
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20The value of where is an integer is:
A.
B.
C.
D.
Correct Answer:
Explanation:When is even, . When is odd, . This is written as .
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21The value of where is an integer is:
A.
B.
C.
D.
Correct Answer:
Explanation:The sine function is zero at all integer multiples of .
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22If in , which coefficients are zero?
A. and
B. only
C. only
D.No coefficients are zero
Correct Answer: and
Explanation: is an odd function. Therefore, the DC component and all cosine coefficients are zero.
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23What is the period of the function ?
A.
B.
C.
D.
Correct Answer:
Explanation:For a function , period . Here , so .
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24In the Fourier series of the square wave defined by for and for , the value of is:
A.
B.
C.
D.
Correct Answer:
Explanation:The defined square wave is an odd function (symmetry about the origin). Therefore, all cosine coefficients () are zero.
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25Which term represents the 'fundamental harmonic' in a Fourier series?
A.The term with
B.The term
C.The term with
D.The term with
Correct Answer: The term with
Explanation:The term corresponding to has the same frequency as the original function's period and is called the fundamental harmonic.
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26Parseval's identity is useful for:
A.Finding the sum of infinite series involving squares of integers.
B.Finding the phase angle of the harmonics.
C.Determining if a function is even or odd.
D.Calculating the derivative of .
Correct Answer: Finding the sum of infinite series involving squares of integers.
Explanation:Parseval's identity relates the integral of the function squared to the sum of squared coefficients. It is frequently used to sum series like .
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27If in , the value of is:
A.
B.
C.
D.
Correct Answer:
Explanation:.
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28The complex coefficient corresponds to:
A.The average value of the function over the period.
B.The amplitude of the fundamental frequency.
C.Zero always.
D.The value of the function at .
Correct Answer: The average value of the function over the period.
Explanation:, which is the mean value (same as ).
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29If the interval of a function is changed from to , the basis functions change from to:
A.
B.
C.
D.
Correct Answer:
Explanation:The argument changes to scale the period from to . The transformation is .
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30Which of the following conditions ensures that the Dirichlet's integral converges?
A.The integral of over the period is finite (Absolute Integrability).
B.The function is continuous everywhere.
C.The function is differentiable everywhere.
D.The function is strictly increasing.
Correct Answer: The integral of over the period is finite (Absolute Integrability).
Explanation:One of the key Dirichlet conditions is that .
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31For a function expanded in a Fourier series, the term represents:
A.The amplitude of the -th harmonic.
B.The phase angle of the -th harmonic.
C.The power of the -th harmonic.
D.The frequency of the -th harmonic.
Correct Answer: The amplitude of the -th harmonic.
Explanation:We can write as , where amplitude .
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32In the Fourier series of in , the coefficients are:
A.
B.
C.
D.
Correct Answer:
Explanation: is an Even function. Even functions have no sine terms, so .
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33What happens to the Fourier series of a discontinuous function near the discontinuity?
A.Gibbs Phenomenon (overshoot)
B.It becomes infinite.
C.It becomes zero.
D.It becomes a straight line.
Correct Answer: Gibbs Phenomenon (overshoot)
Explanation:The Gibbs phenomenon is the oscillatory behavior of the Fourier series near a jump discontinuity, where the partial sums overshoot the function value by about 9%.
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34For the Half Range Sine Series of in , the value of is:
A.
B.
C.
D.
Correct Answer:
Explanation:. This equals .
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35The constant term in the Fourier Series of in is:
A.
B.
C.
D.
Correct Answer:
Explanation:Using trig identity: . This is already a Fourier series. The constant term () is .
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36If is periodic with period , then equals:
A.
B.
C.
D.
Correct Answer:
Explanation:This is the definition of a periodic function.
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37The complex form of the Fourier series is often preferred in signal processing because:
A.It simplifies algebraic manipulations involving derivatives and integrals.
B.It uses only real numbers.
C.It eliminates the DC component.
D.It only works for even functions.
Correct Answer: It simplifies algebraic manipulations involving derivatives and integrals.
Explanation:Exponential functions () are eigenfunctions of differentiation and integration, making algebraic manipulation much easier than with sines and cosines.
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38When expanding as a half-range cosine series in , the period of the extended function is:
A.
B.
C.
D.
Correct Answer:
Explanation:For a half-range series defined on , the extension covers , creating a period of . Here , so .
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39The value of for is:
A.
B.
C.
D.
Correct Answer:
Explanation:The integral of a cosine function over a complete number of periods (or a symmetric interval equal to the period) is zero.
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40For a function defined in , the coefficient is:
A.
B.
C.
D.
Correct Answer:
Explanation:The integration limits change to match the definition interval , but the normalization factor remains the same as in .
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41If is even, then is:
A.Odd
B.Even
C.Periodic but neither even nor odd
D.Constant
Correct Answer: Odd
Explanation:Product of Even () and Odd () is Odd.
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42Identify the relation used to derive the Fourier coefficients:
A.Orthogonality of trigonometric functions.
B.Pythagorean theorem.
C.Taylor series expansion.
D.Laplace transform.
Correct Answer: Orthogonality of trigonometric functions.
Explanation:The formulas for and rely entirely on the fact that , etc.
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43Which series contains only terms with odd harmonics ()?
A.Functions with Half-wave symmetry: .
B.Even functions.
C.Odd functions.
D.Functions with period .
Correct Answer: Functions with Half-wave symmetry: .
Explanation:Half-wave symmetry results in for even , leaving only odd harmonics.
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44The RMS (Root Mean Square) value of a function over is related to Parseval's theorem by:
A.
B.
C.
D.
Correct Answer:
Explanation:Parseval's theorem equates this RMS squared value (average power) to the sum of the squared spectral coefficients.
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45In the Fourier series of in , the function is:
A.Neither even nor odd
B.Even
C.Odd
D.Zero
Correct Answer: Neither even nor odd
Explanation: and . Thus, the series will contain both cosine and sine terms.
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46If is the complex Fourier coefficient, then represents:
A.The power spectrum at frequency .
B.The phase spectrum.
C.The time domain signal.
D.The derivative of the signal.
Correct Answer: The power spectrum at frequency .
Explanation: indicates the power/energy contribution of the frequency component to the total signal.
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47For a half-range cosine series of (constant) in :
A., all other .
B. for all .
C. for all .
D.All coefficients are non-zero.
Correct Answer: , all other .
Explanation:If , it is already an even constant. . The series is just the constant term . No oscillating terms are needed.
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48The sum of the series derived from the Fourier series of a square wave is:
A.
B.
C.
D.
Correct Answer:
Explanation:This is the classic Gregory-Leibniz series, often derived by evaluating the Fourier series of a square wave at a peak.
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49If is continuous and piecewise smooth, the Fourier series converges:
A.Uniformly to .
B.Only at .
C.To infinity.
D.Pointwise but not uniformly.
Correct Answer: Uniformly to .
Explanation:If the periodic function is continuous everywhere and has piecewise continuous derivative, the series converges uniformly.
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50In the expansion of in , the value of is:
A.
B.
C.
D.
Correct Answer:
Explanation: is its own Fourier series. is the coefficient of . All other coefficients are zero.
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