IIT-JAM: Mathematical Methods (2005-2019)

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Questions and Answers

Given a matrix M, which statement being true would indicate that M is its own inverse?

  • The determinant of M is 1.
  • M multiplied by itself equals the identity matrix. (correct)
  • M is orthogonal and symmetric.
  • The trace of M is equal to zero.

If a matrix M is orthogonal, what can be said about its eigenvalues?

  • All eigenvalues must be real and positive.
  • All eigenvalues must be purely imaginary.
  • All eigenvalues must be either +1 or -1. (correct)
  • All eigenvalues must be complex with a magnitude of 1.

A periodic function f(x) is expanded in a Fourier series. If f(x) is an even function, which of the following statements is generally true about the Fourier coefficients?

  • All sine coefficients are zero. (correct)
  • The series contains only a DC component.
  • Both sine and cosine coefficients are non-zero.
  • All cosine coefficients are zero.

Given a matrix P, what operation is performed to obtain the symmetric part of P?

<p>Averaging P with its transpose. (B)</p> Signup and view all the answers

A matrix equation represents an ellipse. What does the semi-major axis length signify about the ellipse?

<p>The longest distance from the center to a vertex. (A)</p> Signup and view all the answers

For a periodic function f(x) with period $2\pi$, expanded as a Fourier series, how are the coefficients typically determined?

<p>By integrating f(x) multiplied by trigonometric functions over one period. (D)</p> Signup and view all the answers

If P and Q are two real, symmetric matrices, under what condition will their product PQ also be symmetric?

<p>Only if P and Q commute, i.e., PQ = QP. (A)</p> Signup and view all the answers

When evaluating the work done by a force over a closed loop, under what condition is the work guaranteed to be zero?

<p>If the force is conservative. (D)</p> Signup and view all the answers

In the context of Fourier series, what characterizes an even function that is defined over a symmetric interval around the origin?

<p>Its Fourier series contains only cosine terms and a constant. (A)</p> Signup and view all the answers

If λ is an eigenvalue of matrix A, what is the eigenvalue of matrix kA, where k is a scalar?

<p>kλ (C)</p> Signup and view all the answers

How is a unit vector normal to the surface of a function $z = f(x, y)$ typically calculated?

<p>By taking the gradient of f and normalizing it. (D)</p> Signup and view all the answers

Which mathematical condition must be met for a matrix to be considered Hermitian?

<p>It must be equal to its conjugate transpose. (A)</p> Signup and view all the answers

Given that P is a Hermitian matrix and Q is a skew-Hermitian matrix, which of the following combinations is necessarily Hermitian?

<p>iPQ (D)</p> Signup and view all the answers

Given a constant vector F and a position vector r, what does the gradient of their dot product, $\nabla (F \cdot r)$, represent?

<p>The constant vector F itself. (D)</p> Signup and view all the answers

To find the inverse of a matrix M, what is the Cayley-Hamilton theorem typically used for?

<p>Expressing the inverse as a polynomial of the matrix. (C)</p> Signup and view all the answers

In solving a differential equation using separation of variables, which condition must be satisfied by the resulting functions?

<p>They must be linearly independent. (A)</p> Signup and view all the answers

When calculating the surface integral of a field over a closed surface, which theorem relates this integral to a volume integral?

<p>Divergence Theorem (Gauss's Theorem). (D)</p> Signup and view all the answers

In cylindrical coordinates, what is a key difference in integrating a vector field compared to Cartesian coordinates?

<p>The differential volume element changes, affecting the integral's value. (D)</p> Signup and view all the answers

If a coordinate transformation involves changing from $(x, y)$ to $(\xi, \eta)$, how does the Jacobian of the transformation relate area elements in the two coordinate systems?

<p>$dx dy = |J| d\xi d\eta$, where |J| is the absolute value of the Jacobian determinant. (B)</p> Signup and view all the answers

Given a matrix M, under which condition are its eigenvectors guaranteed to be orthogonal?

<p>If M is symmetric. (A)</p> Signup and view all the answers

What does Stokes' theorem relate?

<p>A surface integral to a line integral. (D)</p> Signup and view all the answers

How can the stability of a solution to a differential equation typically be assessed?

<p>By analyzing the eigenvalues of the system's matrix. (C)</p> Signup and view all the answers

What concept from vector calculus is essential for simplifying and solving line integrals, especially those involving closed paths?

<p>Curl. (C)</p> Signup and view all the answers

In the context of matrix analysis, what is the significance of the trace of a matrix?

<p>It is the sum of the diagonal elements and equals the sum of the eigenvalues. (C)</p> Signup and view all the answers

In a Taylor series expansion, what is the role of higher-order derivatives in approximating a function?

<p>They improve the accuracy of the approximation, especially away from the expansion point. (A)</p> Signup and view all the answers

When assessing whether a function is continuous at a point using limits, what condition must be satisfied?

<p>The left-hand limit, right-hand limit, and function value at the point must all exist and be equal. (B)</p> Signup and view all the answers

Which condition involving the dot product of a unit vector and a vector in a plane indicates that the unit vector is perpendicular to the plane?

<p>The dot product is zero. (B)</p> Signup and view all the answers

What is a key difference between a scalar field and a vector field?

<p>A scalar field assigns a scalar to each point in space, while a vector field assigns a vector. (B)</p> Signup and view all the answers

When is the flux of a vector field through a closed surface equal to zero, according to the divergence theorem?

<p>When the divergence of the vector field is zero everywhere within the volume enclosed by the surface. (B)</p> Signup and view all the answers

In complex analysis, what is the Cauchy-Riemann equation primarily used for?

<p>To check if a complex function is analytic (differentiable). (D)</p> Signup and view all the answers

Flashcards

Self-Inverse Matrix

A matrix where its inverse equals itself. M = M⁻¹

Symmetric Matrix

A matrix where the transpose equals itself. M = Mᵀ

Hermitian Matrix

A matrix A is Hermitian if it is equal to its conjugate transpose.

Symmetric Part of a Matrix

The symmetric part of a matrix P is (P + Pᵀ)/2.

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Symmetric Matrix

A matrix is symmetric if its transpose is equal to the matrix itself.

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Fourier Series

A Fourier Series is a representation of a periodic function as a sum of sine and cosine functions.

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Hermitian Matrix

A matrix is Hermitian if its conjugate transpose equals itself.

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Skew-Hermitian Matrix

A matrix is skew-Hermitian if its conjugate transpose equals the negative of itself.

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Divergence of Vector Product

If A is a constant vector and r is the position vector, then ∇(A · r) = A.

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Non-Invertible Matrix

If the determinant of given matrix is zero.

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Coordinate Transformation

Represents the relationship between the coordinates x, y and the coordinates (ξ, η)

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Irrigational and Solenoidal Gradient

A gradient that can both rotate/curve and expand.

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Fourier Transform

When a series shows a particular pattern

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Polar Representation

A technique of complex numbers in the form of complex exponents

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Complex Number

A point showing a value of X + iY on Cartesian axis

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Study Notes

  • These are study notes from past IIT-JAM physics exams from 2005-2019, focusing on mathematical methods.

IIT-JAM 2005

  • For a matrix M = (0 1 \ 1 0), being non-orthogonal is incorrect.
  • The eigenvalues of an orthogonal matrix are +1 or -1; in this case, they are 1 and -1
  • Periodic functions: A periodic function f(x) can be expressed as a Fourier series
  • Given ( f(x) = \sum_{n=0}^{\infty} (a_n \cos(nx) + b_n \sin(nx)) ), and functions ( f_1(x) = \cos^2 x ) and ( f_2(x) = \sin^2 x ) expanded in Fourier series with coefficients ( a_n^{(1)}, b_n^{(1)}, a_n^{(2)}, b_n^{(2)} ), then ( a_0^{(1)} = \frac{1}{2} ) and ( a_2^{(2)} = -\frac{1}{2} )

IIT-JAM 2006

  • The symmetric part of a matrix ( P ) can be found using ( \frac{P + P^T}{2} ).
  • Given ( P = \begin{pmatrix} a & a-2b \ b & b \end{pmatrix} ), its symmetric part is ( \begin{pmatrix} a & \frac{a+b-2b}{2} \ \frac{a+b-2b}{2} & b \end{pmatrix} ) =( \begin{pmatrix} a & \frac{a-b}{2} \ \frac{a-b}{2} & b \end{pmatrix} )

IIT-JAM 2007

  • The matrix equation ( \begin{pmatrix} x & y \end{pmatrix} \begin{pmatrix} 5 & -7 \ 7 & 3 \end{pmatrix} \begin{pmatrix} x \ y \end{pmatrix} = 15 ) represents an ellipse with a semi-major axis of ( \sqrt{5} ).
  • For a periodic function ( f(x) ) with period ( 2\pi ) defined as 0 for ( -\pi < x < 0 ) and ( \sin x ) for ( 0 < x < \pi ), the coefficient of ( \cos(2x) ) in its Fourier series expansion is ( -\frac{2}{3\pi} )

IIT-JAM 2008

  • For two real, symmetric matrices ( P ) and ( Q ), the product ( PQ ) is symmetric if ( PQ = QP ).
  • Work done by a force: The work done by a force ( dW = 2xy , dx + x^2 , dy ) for a complete cycle around a unit circle is 0

IIT-JAM 2009

  • The Fourier series of the periodic function f(x) = |sinx| has non-zero coefficients ( \alpha_n ) for even ( n )

IIT-JAM 2010

  • The eigenvalues of the matrix ( M = \frac{1}{\sqrt{2}} \begin{pmatrix} i & 1 \ 1 & i \end{pmatrix} ) are complex with modulus 1.
  • For a surface of revolution ( z = \sqrt{x^2 + y^2} ), the unit vector normal to the surface at point ( \left( \frac{\sqrt{3}}{2}, 0, \frac{1}{2} \right) ) is ( \frac{\sqrt{3}}{5} \hat{i} + 0 \hat{j} - \frac{2}{\sqrt{5}} \hat{k} )

IIT-JAM 2011

  • The line integral ( \oint \vec{F} \cdot d\vec{l} ) where ( \vec{F} = \frac{x}{x^2 + y^2} \hat{x} + \frac{y}{x^2 + y^2} \hat{y} ) along a semi-circular path is 0.
  • The matrix P is Hermitian and Q is skew-Hermitian, then ( P + iQ ) is necessarily a Hermitian matrix.

IIT-JAM 2012

  • ( \nabla(\vec{F} \cdot \vec{r}) ) would be (\vec{F})
  • For a constant vector ( \vec{F} ) and position vector ( \vec{r} ),

IIT-JAM 2013

  • Given ( M = \begin{pmatrix} 0 & 1 & 1 \ 1 & 0 & 1 \ 1 & 1 & 0 \end{pmatrix} ), its inverse is ( M^2 - I )

IIT-JAM 2014

  • Given f(1) = 1, f'(1) = 1, and f''(1) = 1, the value of f(1/2) is approximately 0.606.
  • For vectors ( \vec{a} = \hat{j} + \hat{k} ), ( \vec{b} = 2\hat{i} + 3\hat{j} - 5\hat{k} ), and ( \vec{c} = \hat{j} - \hat{k} ), the vector product ( \vec{a} \times (\vec{b} \times \vec{c}) ) is in the same direction as ( \vec{c} )
  • The value of ( \sum_{n=0}^{\infty} r^n \sin(n\theta) ) for ( r = 0.5 ) and ( \theta = \frac{\pi}{3} ) is ( \frac{1}{\sqrt{3}} )

IIT-JAM 2015

  • For coordinate transformation x' = x+y/√2, y' = x-y/√2, the area elements dx'dy' and dxdy are related by jdxdy where j is -1
  • The trace of a 2x2 matrix is 4 and determinant is 8, if one eigenvalue is 2(1+i) the other eigenvalue is 2(1-i)
  • For a vector field F=yi + xz^3j -zy k, the contour integral value is F⋅dr is 28π

IIT-JAM 2016

  • The phase of the complex number (1+i)i in the polar representation is 3π/4
  • The point (1/2,1/2) represented the complex number 1/1-i

IIT-JAM 2017

  • For Pauli spin matrices, ( \sigma_1 \sigma_2 = i \sigma_3 )
  • The integral of the vector A^(ρ,φ,z) =40/ρ cos^2(φ)ρ over the volume of a cylinder of height L and radius R is 40πRLi.
  • The graph most accurately represents the derivative f'(x) of function f(x) =1/1+x^2

IIT-JAM 2018

  • The line which v^2f=0 is x=2y
  • If the curve is given by r(t)= ti + t^2j +t^3k the unit vector of the tangent to the curve at t=1 is ( i +2j +3k)/ √14
  • -π<x<0 The function f(x) ={-x, 0x<π expanded a Fourier series is expansion true that a ≠ 0, b = 0

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