Sample m.tech(cs)07

Test Code: CS (Short answer type) 2007

M.Tech. in Computer Science

The candidates for M.Tech. in Computer Science will have to take two
tests – Test MIII (objective type) in the forenoon session and Test CS
(short answer type) in the afternoon session. The CS test booklet will have
two groups as follows.

GROUP A

A test for all candidates in analytical ability and mathematics at the B.Sc.
(pass) level, carrying 30 marks.

GROUP B

A test, divided into several sections, carrying equal marks of 70 in
mathematics, statistics, and physics at the B. Sc. (Hons.) level and in
computer science, and in engineering and technology at the B.Tech. level.
A candidate has to answer questions from only one of these sections
according to his/her choice.

The syllabi and sample questions of the CS test are given below.

Note: All questions in the sample set are not of equal difficulty. They
may not carry equal marks in the test.

Syllabus

GROUP A

Elements of set theory. Permutations and combinations. Functions and
relations. Theory of equations. Inequalities.
Limit, continuity, sequences and series, differentiation and integration
with applications, maxima-minima, complex numbers and De Moivre’s
theorem.
Elementary Euclidean geometry and trigonometry.
Elementary number theory, divisibility, congruences, primality.
Determinants, matrices, solutions of linear equations, vector spaces, linear
independence, dimension, rank and inverse.

1

GROUP B

Mathematics
(B.Sc. Hons. level)

In addition to the syllabus of Mathematics in Group A, the syllabus
includes:

Calculus and real analysis – Real numbers, basic properties; convergence
of sequences and series; limits, continuity, uniform continuity of
functions; differentiability of functions of one or more variables and
applications. Indefinite integral, fundamental theorem of Calculus,
Riemann integration, improper integrals, double and multiple integrals and
applications. Sequences and series of functions, uniform convergence.
Linear algebra - Vector spaces and linear transformations; matrices and
systems of linear equations, characteristic roots and characteristic vectors,
Cayley-Hamilton theorem, canonical forms, quadratic forms.
Graph Theory - Connectedness, trees, vertex coloring, planar graphs,
Eulerian graphs, Hamiltonian graphs, digraphs and tournaments.
Abstract algebra – Groups, subgroups, cosets, Lagrange’s theorem; normal
subgroups and quotient groups; permutation groups; rings, subrings,
ideals, integral domains, fields, characteristics of a field, polynomial rings,
unique factorization domains, field extensions, finite fields.
Differential equations – Solutions of ordinary and partial differential
equations and applications.

Statistics
(B.Sc. Hons. level)

Notions of sample space and probability, combinatorial probability,
conditional probability, Bayes theorem and independence, random
variable and expectation, moments, standard univariate discrete and
continuous distributions, sampling distribution of statistics based on
normal samples, central limit theorem, approximation of binomial to
normal. Poisson law, Multinomial, bivariate normal and multivariate
normal distributions.

2

Descriptive statistical measures, product-moment correlation, partial and
multiple correlation; regression (simple and multiple); elementary theory
and methods of estimation (unbiasedness, minimum variance, sufficiency,
maximum likelihood method, method of moments, least squares methods).
Tests of hypotheses (basic concepts and simple applications of Neyman-
Pearson Lemma). Confidence intervals. Tests of regression. Elements of
non-parametric inference. Contingency tables and Chi-square, ANOVA,
basic designs (CRD/RBD/LSD) and their analyses. Elements of factorial
designs. Conventional sampling techniques, ratio and regression methods
of estimation.

Physics
(B.Sc. Hons. level)

General properties of matter – Elasticity, surface tension, viscosity.
Classical Dynamics – Lagrangian and Hamiltonian formulation,
Symmetries and conservation laws, Motion in central field of force,
collision and scattering, mechanics of many system of particles, small
oscillation and normal modes, wave motion, Special theory of relativity.
Electrodynamics – Electrostatics, magnetostatics, electromagnetic
induction, self and mutual inductance, capacitance, Maxwell’s equation in
free space and linear isotropic media, boundary conditions of fields at
interfaces.
Physical optics – Interference, diffraction, polarization.
Nonrelativistic quantum mechanics – Wave particle duality, Heisenberg’s
uncertainty principle, Schrodinger’s equation, particle in a box, harmonic
oscillator, tunneling through a barrier, motion in a central potential, orbital
angular momentum, angular momentum algebra.
Thermodynamics and Statistical Physics – Laws of thermodynamics and
their consequences, thermodynamic potentials and Maxwell’s relations,
chemical potential, phase equilibrium, phase space, microstates and
macrostates, partition function free energy, classical and quantum
statistics.
Electronics – Semiconductor physics, diode as a circuit element, clipping,
clamping, rectification, Zener regulated power supply, transistor as a
circuit element, CC CB CE configuration, transistor as a switch, OR and
NOT gates feedback in amplifiers.
Operational Amplifier and its applications – Inverting, noninverting
amplifiers, adder, integrator, differentiator, waveform generator
comparator and Schmitt trigger.
Digital integrated circuits – NAND, NOR gates as building blocks, XOR
gates, combinational circuits, half and full adder.
3

Atomic and molecular physics – Quantum states of an electron in an atom,
Hydrogen atom spectrum, electron spin, spin–orbit coupling, fine
structure, Zeeman effect, Lasers.
Condensed matter physics – Crystal classes, 2D and 3D lattice, reciprocal
lattice, bonding, diffraction and structure factor, point defects and
dislocations, lattice vibration, free electron theory, electron motion in
periodic potential, energy bands in metals, insulators and semiconductors,
Hall effect, thermoelectric power, electron transport in semiconductors,
dielectrics, Claussius Mossotti equation, Piezo, pyro and ferro electricity.
Nuclear and particle physics – Basics of nuclear properties, nuclear forces,
nuclear structures, nuclear reactions, interaction of charged particles and
e-m rays with matter, theoretical understanding of radioactive decay,
particle physics at the elementary level.

Computer Science
(B.Tech. level)

Data structure – Arrays, stack, queue, linked list, binary tree, heap, AVL
tree, B-tree.
Programming languages – Fundamental concepts, abstract data types,
procedure call and parameter passing, languages like C and C++.
Design and analysis of algorithms – Sorting, selection, searching.
Computer organization and architecture – Number representation,
computer arithmetic, memory organization, I/O organization,
microprogramming, pipelining, instruction level parallelism.
Operating systems – Memory management, processor management,
critical section, deadlocks, device management.
Formal languages and automata theory – Finite automata and regular
expression, pushdown automata, context-free grammars, Turing machines,
elements of undecidability.
Principles of Compiler Construction – Lexical analyzer, parser, code
optimization, symbol table.
Database management systems – Relational model, relational algebra,
relational calculus, functional dependency, normalization (up to 3rd
normal form).
Computer networks – OSI, TCP/IP protocol; internetworking; LAN
technology – Bus/tree, Ring, Star; MAC protocols; WAN technology -
Circuit switching, packet switching; data communications, data encoding,
routing, flow control, error detection/correction.

4

Switching Theory and Logic Design – Boolean algebra, minimization of
Boolean functions, combinational and sequential circuits – synthesis and
design.

Engineering and Technology
(B.Tech. level)

Moments of inertia, motion of a particle in two dimensions, elasticity,
friction, strength of materials, surface tension, viscosity and gravitation.
Laws of thermodynamics, and heat engines.
Electrostatics, magnetostatics and electromagnetic induction.
Magnetic properties of matter – dia, para and ferromagnetism.
Laws of electrical circuits – RC, RL and RLC circuits, measurement of
current, voltage and resistance.
D. C. generators, D. C. motors, induction motors, alternators, transformers.
p-n junction, bipolar & FET devices, transistor amplifier, oscillator, multi-
vibrator, operational amplifier.
Digital circuits – Logic gates, multiplexer, de-multiplexer, counter, A/D
and D/A converters.
Boolean algebra, minimization of switching function, combinational and
sequential circuits.
Microprocessor/assembly language programming, C.

5

Sample Questions

GROUP A

Mathematics

A1. If 1, a1, a2,…, an-1 are the n roots of unity, find the value of
(1 - a1) (1 - a2)…(1 - an-1).

A2. Let
S ={( a1 , a2 , a3 , a4 ) : ai ∈ℜ, i =1, 2, 3, 4 and a1 + a2 + a3 + a4 = 0}
and
Γ = {( a1 , a2 , a3 , a4 ) : ai ∈ℜ, i =1, 2, 3, 4 and a1 − a2 + a3 − a4 = 0}.
Find a basis for S ∩ Γ .

A3. Provide the inverse of the following matrix:

 c 0 c1 c2 c3 
 
 c 2 c3 c0 c1 
c − c c1 − c0 
 3 2

c − c c3 − c2 
 1 0 
1+ 3 3+ 3 3− 3 1− 3
c0= , c1 = , c2= , c3 = .
where 4 2 4 2 4 2 and 4 2
(Hint: What is c 0 + c12 + c 2 + c3 ?)
2 2 2

A4. For any real number x and for any positive integer n show that

[ x] +  x + 1  +  x + 2  +  +  x + n − 1 = [ nx]
     
 n  n  n 
where [a] denotes the largest integer less than or equal to a.

A5. Let bqbq-1…b1b0 be the binary representation of an integer b, i.e.,
q
b = ∑ 2 j b j , bj = 0 or 1, for j = 0, 1, …, q.
j =0

Show that b is divisible by 3 if b0 − b1 + b2 −  +(−1) bq = 0 .
q

A6. A sequence {xn} is defined by x1 = 2, xn+1 = 2 + x n , n =1,2, …
Show that the sequence converges and find its limit.
6

A7. Is sin ( x | x | ) differentiable for all real x? Justify your answer.

A8. Find the total number of English words (all of which may not have
proper English meaning) of length 10, where all ten letters in a word
are not distinct.

a1 a 2 a
A9. Let a0 + + + ..... + n = 0, where ai’s are some real constants.
2 3 n +1
Prove that the equation a 0 + a 1 x + a 2 x 2 + ... + a n x n = 0 has at least one
solution in the interval (0, 1).

A10. Let φ(n) be the number of positive integers less than n and having no
common factor with n. For example, for n = 8, the numbers 1, 3, 5, 7
have no common factors with 8, and hence φ(8) = 4. Show that
(i) φ ( p ) = p − 1 ,
(ii) φ ( pq ) = φ ( p )φ ( q ) , where p and q are prime numbers.

A11. A set S contains integers 1 and 2. S also contains all integers of the
form 3x+ y where x and y are distinct elements of S, and every
element of S other than 1 and 2 can be obtained as above. What is S?
Justify your answer.

A12. Let f be a real-valued function such that f(x+y) = f(x) + f(y) ∀x, y ∈
R. Define a function φ by φ(x) = c + f(x), x ∈ R, where c is a
real constant. Show that for every positive integer n,
φ n ( x ) = (c + f ( c ) + f 2 (c) + ..... + f n −1 (c)) + f n ( x );

where, for a real-valued function g, g n (x) is defined by
g 0 ( x ) = 0, g 1 ( x) = g ( x), g k +1 ( x ) = g ( g k ( x)).

A13.Consider a square grazing field with each side of length 8 metres.
There is a pillar at the centre of the field (i.e. at the intersection of the two
8
diagonals). A cow is tied with the pillar using a rope of length 3 metres.
Find the area of the part of the field that the cow is allowed to graze.

A14.Let f : [0,1] → [-1,1] be such that f(0) = 0 and f(x) = sin 1 for x > 0. Is
x
it possible to get three sequences {an}, {bn}, {cn} satisfying all the three

7

properties P1, P2 and P3 stated below? If so, provide an example sequence
for each of the three sequences. Otherwise, prove that it is impossible to
get three such sequences.

P1: an > 0, bn > 0, cn > 0, for all n.

P2: n → ∞ an = 0, n → ∞ bn = 0, n → ∞ cn = 0.
lim lim lim

P3: n → ∞ f (an ) = 0, n → ∞ f (bn ) = 0.5, n → ∞ f (cn ) = 1.
lim lim lim

A15. Let a1 a2 a3… ak be the decimal representation of an integer a
(a1∈{0,…,9} for i = 1,2, …, k). For example, if a = 1031, then
a1=1, a2=0, a3=3, a4=1. Show that a is divisible by 11 if and only
if
∑a - ∑a i i
i odd i even

is divisible by 11.

GROUP B

Mathematics

x n +3
M1. Let 0 < x1 < 1. If xn+1 = , n = 1,2,3, …
3x n + 1
5x n +3
(i)Show that xn+2 = , n = 1,2,3, …
3x n + 5
(ii)Hence or otherwise, show that n → ∞ xn exists.
lim

(iii)Find n → ∞ xn .
lim

M2. (a) A function f is defined over the real line as follows:
 x sin π , x > 0
f ( x) =  x

0, x = 0.
Show that f ′(x ) vanishes at infinitely many points in (0,1).

8

(b) Let f : [0,1] → ℜ be a continuous function with f(0) = 0. Assume
that f ′ is finite and increasing on (0,1).
Let g ( x) = f (xx ) x ∈ (0,1) . Show that g is increasing.

M3. Let a1=1, and
an = n(an-1+1) for n = 2, 3, …
Let Pn = (1 + a1 )(1 + a 2 )(1 + a n )
1 1 1

Find n → ∞ Pn .
lim

M4. Consider the function of two variables
F(x,y) = 21x - 12x2 - 2y2 + x3 + xy2.
(a)Find the points of local minima of F.
(b)Show that F does not have a global minimum.

M5. Find the volume of the solid given by 0 ≤ y ≤ 2 x , x 2 + y 2 ≤ 4 and
0≤ z≤ x.

M6. (a) Let A, B and C be 1×n, n×n and n×1 matrices respectively. Prove
or disprove: Rank(ABC) ≤ Rank(AC).
(b) Let S be the subspace of R4 defined by
S = {(a1, a2, a3, a4) : 5a1 - 2a3 -3a4 = 0}.
Find a basis for S.

M7. Let A be a 3×3 matrix with characteristic equation λ3 − 5λ2 = 0.

(i)Show that the rank of A is either 1 or 2.
(ii)Provide examples of two matrices A1 and A2 such that the rank of
A1 is 1, rank of A2 is 2 and Ai has characteristic equation λ3 - 5λ2 = 0
for i = 1, 2.

M8. Define B to be a multi-subset of a set A if every element of B is an el-
ement of A and elements of B need not be distinct. The ordering of
elements in B is not important.

For example, if A = {1,2,3,4,5} and B = {1,1,3}, B is a 3-element
multi-subset of A. Also, multi-subset {1,1,3} is the same as the mul-
ti-subset {1,3,1}.

9

(a) How many 5-element multi-subsets of a 10-element set are possi-
ble?
(b) Generalize your result to m-element multi-subsets of an n-ele-
ment set (m < n).

M9. Consider the vector space of all n x n matrices over ℜ .

(a) Show that there is a basis consisting of only symmetric and
skew-symmetric matrices.
(b) Find out the number of skew-symmetric matrices this basis
must contain.

M10. Let R be the field of reals. Let R[x] be the ring of polynomials over
R, with the usual operations.
(a) Let I ⊆ R[x] be the set of polynomials of the form a0 +a1x +....
+ anxn with a0 = a1 = 0. Show that I is an ideal.
(b) Let P be the set of polynomials over R of degree ≤ 1. Define ⊕
and Θ on P by (a0 +a1x) ⊕ (b0 +b1 x) = (a0 + b0)+(a1 +b1)x and
(a0 +a1x) Θ (b0 + b1x) = a0b0 + (a1b0 +a0b1)x. Show that (P, ⊕,
Θ ) is a commutative ring. Is it an integral domain? Justify your
answer.
M11. (a) If G is a group of order 24 and H is a subgroup of G of order
12, prove that H is a normal subgroup of G.
(b) Show that a field of order 81 cannot have a subfield of order 27.

M12. (a) Consider the differential equation:
d2y dy
2
cos x + sin x − 2 y cos 3 x = 2 cos5 x.
dx dx
By a suitable transformation, reduce this equation to a second
order linear differential equation with constant coefficients.
Hence or otherwise solve the equation.
(b) Find the surfaces whose tangent planes all pass through the
origin.
M13.(a) Draw a simple graph with the degree sequence (1,1,1,1,4).
(b) Write down the adjacency matrix of the graph.
(c) Find the rank of the above matrix.
(d) Using definitions of characteristic root and characteristic vectors
only, find out all the characteristic roots of the matrix in (b).

10

M14. (a) Show that a tree on n vertices has at most n−2 vertices with
degree > 1.
(b) Show that in an Eulerian graph on 6 vertices, a subset of 5
vertices cannot form a complete subgraph.

M15. (a) Show that the edges of K4 can be partitioned into 2 edge-disjoint
spanning trees.
(b) Use (a) to show that the edges of K6 can be partitioned into 3
edge-disjoint spanning trees.
(c) Let Kn denote the complete undirected graph with n vertices and
let n be an even number. Prove that the edges of Kn can be
partitioned into exactly n/2 edge-disjoint spanning trees.

Statistics

S1. (a) X and Y are two independent and identically distributed random
variables with Prob[X = i] = pi, for i = 0, 1, 2, ……… Find
Prob[X < Y] in terms of the pi values.

(b)Based on one random observation X from N(0, σ2), show that √π/
2 |X| is an unbiased estimate of σ.

S2. (a) Let X0, X1, X2, … be independent and identically distributed
random variables with common probability density function f. A
random variable N is defined as
N = n if X1 ≤ X 0 , X 2 ≤ X 0 , , X n−1 ≤ X 0 , X n > X 0 , n = 1, 2, 3,

Find the probability of N = n .

(b) Let X and Y be independent random variables distributed
uniformly over the interval [0,1]. What is the probability that
X
the integer closest to Y is 2?

S3. If a die is rolled m times and you had to bet on a particular number of
sixes occurring, which number would you choose? Is there always
one best bet, or could there be more than one?

11

S4. Let X 1 , X 2 and X3 be independent random variables with Xi
following a uniform distribution over (0, iθ), for i = 1 , 2, 3 . Find
the maximum likelihood estimate of θ based on observations
x1 , x2 , x3 on X 1 , X 2 , X 3 respectively. Is it unbiased? Find the
variance of the estimate.

S5. New laser altimeters can measure elevation to within a few inches,
without bias. As a part of an experiment, 25 readings were made on
the elevation of a mountain peak. These averaged out to be 73,631
inches with a standard deviation (SD) of 10 inches. Examine each of
the following statements and ascertain whether the statement is true
or false, giving reasons for your answer.
(a)73631 ± 4 inches is a 95% confidence interval for the elevation
of the mountain peak.
(b)About 95% of the readings are in the range 73631 ± 4 inches.
(c)There is about 95% chance that the next reading will be in the
range of 73631 ± 4 inches.

S6. Consider a randomized block design with two blocks and two
treatments A and B. The following table gives the yields:

Treatment A Treatment B
Block 1 a b
Block 2 c d

(a)How many orthogonal contrasts are possible with a, b, c and d?
Write down all of them.
(b)Identify the contrasts representing block effects, treatment effects
and error.
(c)Show that their sum of squares equals the total sum of squares.

S7. Let X be a discrete random variable having the probability mass
function
p (x) = Λx(1- Λ)1-x, x = 0, 1,
where Λ takes values ≥ 0.5 only. Find the most powerful test, based
1 2
on 2 observations, for testing H0 : Λ = against H1 : Λ = , with
2 3
level of significance 0.05.

12

S8. (a) Let Xi, i = 1,2,3,4 be independently and identically distributed
N(μ,σ2) random variables. Obtain three non-trivial linear
combinations of X1, X2, X3, X4 such that they are also independently
and identically distributed.
(b) Let X be a continuous random variable such that X and -X are
identically distributed. Show that the density function of X is
symmetric.

S9. Let t1, t2, …tk be k independent and unbiased estimators of the same
k
ti
parameter θ with variances σ 1 ,σ 2 ,σ k . Define t as ∑ . Find E(
2 2 2

i =1 k
k

t ) and the variance of t . Show that ∑ (t
i =1
i − t ) 2 /{k (k − 1)} is an

unbiased estimator of var( t ).

S10. Consider a simple random sample of n units, drawn without
replacement from a population of N units. Suppose the value of Y1 is
unusually low whereas that of Yn is very high. Consider the following
estimator of Y , the population mean.

 y + c, if the sample contains unit 1 but not unit N ;
ˆ =  y − c, if the sample contains unit N but not unit 1;
Y 
 y , for all other samples;

where y is sample mean and c is a constant. Show that Y isˆ
unbiased. Given that
ˆ S2 2c 
V (Y ) = (1 − f ) − (Y N −Y 1− nc)
 n N −1 
n 1 N
where f =
N
and S =
2
∑ (Yi − Y ) 2 , comment on the choice
N − 1 i =1
of c.

S11. In order to compare the effects of four treatments A, B, C, D, a block
design with 2 blocks each having 3 plots was used. Treatments A, B,
C were given randomly to the plots of one block and treatments A,
B, D were given randomly to the plots of the other block. Write
down a set of 3 orthogonal contrasts with the 4 treatment effects and
show that all of them are estimable from the above design.

13

S12. Let X1, X2, …Xn (Xi= (xi1, xi2, …, xip), i=1, 2, …, n) be n random
samples from a p-variate normal population with mean vector µ and
covariance matrix I.

Further, let S = ((sjk)) denote the sample sums of squares and
products matrix, namely
s jk = ∑i =1 ( xij − x j )( xik − x k ),1 ≤ j , k ≤ p, where
n

1 n
xj = ∑ xij ,1 ≤ j ≤ p.
n i =1
Obtain the distribution of  ' S where  ∈ ℜ k ,  ≠ 0.

4
S13. Let Yi = ∑ β j X ij + ∈i , i = 1,2,, k ,
j =1

where Yi’s and X’ijs are known, and ∈i’s are independent and each
∈i’s follows N(0,σ2).

Derive the likelihood ration tests for the following hypotheses
indicating their distributions under the respective null hypothesis.

(a) H0: β2 = 3β1 against H1: β2 = 3β1, and

(b) H0: β1 = β2, β3 = β4, β3 = 2β2 against

H1: at least one of the equalities in H0 is not true

S14. For the following sampling scheme, compute the first and second
order inclusion probabilities:

From a group of 15 male and 10 female students, one male and one
female students are selected using SRS. After these selections, from
the remaining 23 students, two are chosen using SRSWR, thus
selecting a sample of size 4.

Physics

P1. In a photoelectric emission experiment, a metal surface was
successively exposed to monochromatic lights of wavelength λ1, λ2
and λ3. In each case, the maximum velocity of the emitted photo
14

electrons was measured and found to be α, β and γ, respectively. λ3
was 10% higher in value than λ1, whereas λ2 was 10% lower in value
than λ1. If β : γ = 4 : 3, then show that α : β = 9√3 : 8√5.

2
P2. (a) Two bodies A and B have constant heat capacities 2C and 3 C
respectively. The initial temperatures of A and B are 3T and
2T , respectively, in Kelvin scale. A refrigerator working be-
TΟ
tween these two bodies cools down B to a temperature of 4
K.
What is the minimum amount of work required to do this?

(b) A 60Ω resistor carrying a current of 4 ampere for 11seconds is
kept at a constant temperature of 47 Ο C by a stream of cooling
water. Calculate the change in entropy of (i) the resistor, and (ii)
the universe.

P3. The nucleus BZA decays by alpha ( He2 ) emission with a half-life T
4

A− 4
to the nucleus C Z −2 which in turn, decays by beta (electron) emis-
T −
sion with a half-life to the nucleus DZA−14 . If at time t = 0 , the de-
4
cay chain B → C → D had started with B0 number of B nuclei
only, then find out the time t at which the number of C nuclei will
be maximum.

P4. p1 and p 2 are two relativistic protons traveling along a straight line in
n 14n
the same direction with kinetic energies , and fractions
n +1 14n + 1
of their respective total energies. Upon entering a region where a
uniform magnetic field B acts perpendicularly on both, p1 and p 2
describe circular paths of radii r1 and r2 respectively. Determine the
r1
ratio ρ = . What is the value of ρ when n = 5 ?
r2

P5. (a)A mass m is attached to a massless spring of spring constant K via
a frictionless pulley of radius R and mass M as shown in following
Figure. The mass m is pulled down through a small distance x and
released, so that it is set into a simple harmonic motion. Find the
frequency of the vertical oscillation of the mass m.
15

(b) The Hamiltonian of a mechanical system having two degrees of
freedom is:
1 1
H(x, y; px, py) = (px2 + py2) + m ω2(x2 + y2),
2m 2
where m and ω are constants; x, y are the generalized co-ordinates
for which px, py are the respective conjugate momenta.
Show that the expressions (x py -y px)n, n=1,2,3,… are
constants of motion for this system.

P6. In a Millikan's oil drop experimental setup, two small negatively
charged spherical oil droplets having radii 3r and 5r were allowed to
fall freely in the closed chamber filled with air. The downward
terminal velocities attained by them were v1 and v2 respectively.
Subsequently, under the action of a strong electric field, the droplets
attained upward terminal velocities v1/6 and v2/20 respectively.
Neglecting the bouyant force of air and assuming the charges to be
uniformly distributed over the surface of the droplets, compare their
surface charge densities.

P7. An electron is confined to move within a linear interval of length L.
Assuming the potential to be zero throughout the interval except for
the two end points, where the potential is infinite, find the following:

(a) probability of finding the electron in the region 0 < x < L/4, when
it is in the lowest (ground) state of energy;
(c)taking the mass of the electron me to be 9 × 10-31 Kg, Planck's
constant h to be 6.6 × 10-34 Joule-sec and L = 1.1 cm, determine the
electron's quantum number when it is in the state having an energy
equal to 5 × 10-32 Joule.

16

P8. Two blocks of impedance Z1 and Z2 and an inductor L are connected
1000
in series across a supply of 300V, Hz as shown low. The upper
2π
1000
3dB frequency of Z1 alone is Hz and the lower 3dB frequency
2π
1000
of Z2 alone is also Hz. Calculate:
2π
(a) the power dissipated in the circuit, and
(b) the power factor.

P9. (a) Given the circuit shown in the figure, find out the current through
the resistance R = 3Ω between A and B .

(b) Suppose a metal ring of mean radius 100 cm is made of iron and
steel as shown in the figure. The cross-section of the ring is 10
sq.cm. If the ring is uniformly wound with 1000 turns, calculate
the current required to produce a flux of 1 milliweber. The abso-
lute permeability of air is 4π × 10 −7 H/m and relative permeabili-
ty of iron and steel are 250 and 1000 , respectively.

17

P10. (a) Calculate the donor concentration of an n-type Germanium
specimen having a specific resistivity of 0.1 ohm-metre at
300K, if the electron mobility µe = 0.25 metre2/Volt-sec at
300K, and the magnitude of the electronic charge is 1.6 × 10-19
Coulomb.

(b) An n-type Germanium specimen has a donor density of 1.5×1015
cm-3. It is arranged in a Hall effect experiment where the
magnitude of the magnetic induction field B is 0.5Weber/metre2
and current density J = 480 amp/metre2. What is the Hall
voltage if the specimen is 3 mm thick?

P11. Two heavy bodies A and B , each having charge − Q , are kept
rigidly fixed at a distance 2a apart. A small particle C of mass m
and charge + q ( << Q ), is placed at the midpoint of the straight
line joining the centers of A and B . C is now displaced slightly
along a direction perpendicular to the line joining A and B , and
then released. Find the period of the resultant oscillatory motion of
C , assuming its displacement y << a .
If instead, C is slightly displaced towards A , then find the instan-
a
taneous velocity of C , when the distance between A and C is .
2

P12. An elementary particle called ∑-, at rest in laboratory frame,
decays spontaneously into two other particles according to
Σ − → π − + n . The masses of ∑-, π- and n are M1, m1, and m2
respectively.
(a)How much kinetic energy is generated in the decay process?
(b)What are the ratios of kinetic energies and momenta of π − and
n?

18

P13. Consider the following truth table where A, B and C are Boolean
inputs and T is the Boolean output.

A B C T
0 0 0 1
0 0 1 0
0 1 0 0
0 1 1 1
1 0 0 0
1 0 1 1
1 1 0 0
1 1 1 1

Express T in a product-of-sum form and hence, show how T can be
implemented using NOR gates only.

P14. (a) Find the relationship between L, C and R in the circuit shown in
the figure such that the impedance of the circuit is independent
of frequency. Find out the impedance.

(b) Find the value of R and the current flowing through R shown in
the figure when the current is zero through R′.

19

τ B (τ )
P15. A gas obeys the equation of state P = + where B(τ ) is a
V V2
function of temperature τ only. The gas is initially at temperature
τ and volume V0 and is expanded isothermally and reversibly to
volume V1 = 2V0 .
(a) Find the work done in the expansion.
(b) Find the heat absorbed in the expansion.
 ∂S   ∂P 
(Hint: Use the relation   =   where the symbols have
 ∂V τ  ∂τ V
their usual meaning.

P16. (a) From the Earth, an observer sees two very high speed rockets
A
and B moving in a straight line in the same direction with
c 2c
velocities and respectively. What is the velocity of B
2 3
relative to A? Here, c denotes the speed of light in vacuum.

(b) Two objects having rest masses m1 and m2 move with
relativistic speeds. Their total energies are E1 and E2 and
kinetic energies are K1 and K2 respectively. If 2m2E1=5m1E2
and K1 is only 5% less than E1, find the value of K2 in terms of
E2.

1 0 
P17. Consider the spin angular momentum operator σz=   0 −1 for

 
1 0
which α =   and β =   are the two eigen states with
0 1
   
eigenvalues +1 and –1 respectively. Calculate the expectation
2 1
value and variance of σz for the state ψ = α + β.
3 3

Computer Science

C1. (a) A grammar is said to be left recursive if it has a non-terminal A
such that there is a derivation A ⇒ + Aα for some sequence of

20

symbols α. Is the following grammar left-recursive? If so, write
an equivalent grammar that is not left-recursive.

A → Bb A→a
B →Cc B→b
C → Aa C→c

(b) An example of a function definition in C language is given
below:
char fun (int a, float b, int c)
{ /* body */ … }
Assuming that the only types allowed are char, int, float
(no arrays, no pointers, etc.), write a grammar for function
headers, i.e., the portion char fun(int a, …) in the
above example.

(c) Consider the floating point number representation in C
programming language.
Give a regular expression for it using the following convention:
l denotes a letter, d denotes a digit, S denotes sign and p
denotes point.
State any assumption that you may need to make.

C2. The following functional dependencies are defined on the
relation ℜ( A, B, C , D, E , F ) :
(a) Find the candidate keys for ℜ .
(b) Is ℜ normalized? If not, create a set on normalized
relations by decomposing ℜ using only the given set of
functional dependencies.
(c) If a new attribute F is added to ℜ to create a new relation
ℜ′( A, B, C , D, E , F ) without any addition to the set of
functional dependencies, what would be the new set of
candidate key for ℜ′ ?
(d) What is the new set of normalized relations that can be derived
by decomposing ℜ′ for the same set of functional
dependencies?
(e) If a new dependency is declared as follows:
For each value of A , attribute F can have two values,
what would be the new set of normalized relations that can be
created by decomposing ℜ′ ?

21

C3.(a) A relation R(A, B, C, D) has to be accessed under the query
σB=10(R). Out of the following possible file structures, which one should be
chosen and why?
i)R is a heap file.
ii)R has a clustered hash index on B.
iii)R has an unclustered B+ tree index on (A, B).

(b) If the query is modified as πA,B(σB=10(R)), which one of the three
possible file structures given above should be chosen in this
case and why?

(c) Let the relation have 5000 tuples with 10 tuples/page. In case of
a hashed file, each bucket needs 10 pages. In case of B+ tree,
the index structure itself needs 2 pages. If the disk needs 25
msecs. to read or write a disk page, what would be the disk
access time for answering the above queries?

C4. Let A and B be two arrays, each of size n. A and B contain numbers
in sorted order. Give an O(log n) algorithm to find the median of
the combined set of 2n numbers.

C5. (a) Consider a pipelined processor with m stages. The processing
time at every stage is the same. What is the speed-up achieved
by the pipelining?
(b) In a certain computer system with cache memory, 750 ns
(nanosec) is the access time for main memory for a cache miss
and 50 ns is the access time for a cache hit. Find the percentage
decrease in the effective access time if the hit ratio is increased
from 80% to 90%.

C6. (a) A disk has 500 bytes/sector, 100 sectors/track, 20 heads and
1000 cylinders. The speed of rotation of the disk is 6000 rpm.
The average seek time is 10 millisecs. A file of size 50 MB is
written from the beginning of a cylinder and a new cylinder
will be allocated only after the first cylinder is totally occupied.
i)Find the maximum transfer rate.
ii)How much time will be required to transfer the file of 50 MB
written on the disk? Ignore the rotational delay but not the seek
time.

(b) Consider a 4-way traffic crossing as shown in the figure.
Suppose that we model the crossing as follows:
22

- each vehicle is modeled by a process,
- the crossing is modeled as a shared data structure. Assume that
the vehicles can only move straight through the intersection (no
left or right turns). Using read-write locks (or any standard
synchronization primitive), you have to device a
synchronization scheme for the processes. Your scheme should
satisfy the following criteria:
i) prevent collisions,
ii) prevent deadlock, and
iii) maximize concurrency but prevent indefinite waiting
(starvation).
Write down the algorithm that each vehicle must follow in order
to pass through the crossing. Justify that your algorithm satisfies
the given criteria.

C7. (a) A computer on a 6 Mbps network is regulated by a token
bucket. The bucket is filled at a rate of 2 Mbps. It is initially
filled to capacity with 8 Megabits. How long can the computer
transmit at the full 6 Mbps?
(b) Sketch the Manchester encoding for the bit stream
0001110101.
(c) If delays are recorded in 8-bit numbers in a 50-router network,
and delay vectors are exchanged twice a second, how much
bandwidth per (full-duplex) line is consumed by the
distributed routing algorithm? Assume that each router has 3
lines to other routers.

23

C8. Consider a binary operation shuffle on two strings, that is just like
shuffling a deck of cards. For example, the operation shuffle on
strings ab and cd, denoted by ab || cd, gives the set of strings
{abcd, acbd, acdb, cabd, cadb, cdab}.

(a) Define formally by induction the shuffle operation on any two
strings x, y ∈ Σ*.
(b) Let the shuffle of two languages A and B, denoted by A || B be
the set of all strings obtained by shuffling a string x ∈ A with a
string y ∈ B. Show that if A and B are regular, then so is A || B.

C9. (a) Give a method of encoding the microinstructions (given in the
table below) so that the minimum number of control bits are
used and maximum parallelism among the microinstructions
is achieved.

Microinstructions Control signals
I1 C1 , C2 , C3 , C4 , C5 , C6 ,
I2 C1 , C3 , C4C6 ,
I3 C2 , C5 , C6 ,
I4 C4 , C5 , C8 ,
I5 C7 , C8 ,
I6 C1 , C8 , C9 ,
I7 C3 , C4 , C8 ,
I8 C1 , C2 , C9 ,

(b) A certain four-input gate G realizes the switching function G(a,
b, c, d) = abc + bcd. Assuming that the input variables are
available in both complemented and uncomplemented forms:
Σ (0, 1, 6, 9,
(i)Show a realization of the function f(u, v, w, x) =
10, 11, 14, 15) with only three G gates and one OR gate.
(ii)Can all switching functions be realized with {G, OR} logic
set ?

C10. Consider a set of n temperature readings stored in an array T. As-
sume that a temperature is represented by an integer. Design an O(n
+ k log n) algorithm for finding the k coldest temperatures.

24

C11. Assume the following characteristics of instruction execution in a
given computer:
• ALU/register transfer operations need 1 clock cycle each,
• each of the load/store instructions needs 3 clock cycles, and
• branch instructions need 2 clock cycles each.

(a) Consider a program which consists of 40% ALU/register
transfer instructions, 30% load/store instructions, and 30%
branch instructions. If the total number of instructions in this
program is 10 billion and the clock frequency is 1 GHz, then
compute the average number of cycles per instruction (CPI),
total execution time for this program, and the corresponding
MIPS rate.
(b) If we now use an optimizing compiler which reduces the total
number of ALU/register transfer instructions by a factor of 2,
keeping the number of other instruction types unchanged, then
compute the average CPI, total time of execution and the
corresponding MIPS rate for this modified program.

C12. A tape S contains n records, each representing a vote in an election.
Each candidate for the election has a unique id. A vote for a
candidate is recorded as his/her id.
(i) Write an O(n) time algorithm to find the candidate who wins
the election. Comment on the main memory space required by
your algorithm.
(ii) If the number of candidates k is known a priori, can you
improve your algorithm to reduce the time and/or space
complexity?
(iii)If the number of candidates k is unknown, modify your
algorithm so that it uses only O(k) space. What is the time
complexity of your modified algorithm?

C13. (a) The order of a regular language L is the smallest integer k for
which Lk = Lk+1, if there exists such a k, and ∞ otherwise.
(i)What is the order of the regular language a + (aa)(aaa)*?
(ii)Show that the order of L is finite if and only if there is an integer
k such that Lk = L*, and that in this case the order of L is the
smallest k such that Lk = L*.
(b)Solve for T(n) given by the following recurrence relations:
T(1) = 1;
T(n) = 2T(n/2) + n log n, where n is a power of 2.

25

(c) An A.P. is {p + qn|n = 0, 1, . . .} for some p, q ∈ IN . Show
that if L ⊆ {a}* and {n| an ∈ L} is an A.P., then L is regular.

C14. (a) You are given an unordered sequence of n integers with many
duplications, such that the number of distinct integers in the
sequence is O(log2 n). Design a sorting algorithm and its
necessary data structure(s), which can sort the sequence using
at most O(n log2(log2 n)) time. (You have to justify the time
complexity of your proposed algorithm.)

(b) Let A be a real-valued matrix of order n x n already stored in
memory. Its (i, j)-th element is denoted by a[i, j]. The
elements of the matrix A satisfy the following property:
Let the largest element in row i occur in column li. Now, for
any two rows i1, i2, if i1 < i2, then li1 ≤ li2 .

2 6 4 5 3
5 3 7 2 4
4 2 1 7 8
0
6 4 5 9 7
3 7 6 8 12

(a)

Row l(i)
I
1 2
2 3
3 3
4 4
5 5

(b)

Figure shows an example of (a) matrix A, and (b) the
corresponding values of li for each row i.

Write an algorithm for identifying the largest valued
element in matrix A which performs at most O(nlog2n)
comparisons.

26

C15. (a) You are given the following file abc.h:

#include <stdio.h>
#define SQR(x) (x*x)
#define ADD1(x) (x=x+1)
#define BeginProgram int main(int argc,char *argv[]){
#define EndProgram return 1; }

For each of the following code fragments, what will be the
output?
(i) #include "abc.h"
main() { int y = 4; printf("%dn", SQR(y+1)); }
(ii) #include "abc.h"
BeginProgram
int y=3; printf("%dn", SQR(ADD1(y)));
EndProgram

(b) Given the following program:
#include <iostream.h>
main()
{
cout<<"MTech (CS)n";
}

Without changing the main() in any way, modify the
program to
produce the following output:

Sample Question
MTech (CS)
Indian Statistical Institute

Engineering and Technology

E1. A bullet of mass M is fired with a velocity of 40 m/s at an angle θ
with the horizontal plane. At P, the highest point of its trajectory,
the bullet collides with a bob of mass 3M suspended freely by a
27

3
mass-less string of length m. After the collision, the bullet gets
10
stuck inside the bob and the string deflects with the total mass
through an angle of 120o keeping the string taut. Find
(i) the angle θ, and
(ii) the height of P from the horizontal plane.
Assume, g = 10 m / s 2 m, and friction in air is negligible.

E2. A rod of length 120 cm is suspended from the ceiling horizontally
by two vertical wires of equal length tied to its ends. One of the
wires is made of steel and has cross-section 0.2 cm 2 and the other
one is of brass having cross-section 0.4 cm 2 . Find out the position
along the rod where a weight may be hung to produce equal stress
in both wires

E3. A chain of total length L = 4 meter rests on a table top, with a part
of the chain hanging over the edge, as shown in the figure below.
Let α be the ratio of the length of the overhanging part of the chain
to L.

If the coefficient of friction between the chain and the table top is
0.5, find the values of α for which the chain remains stationary. If α
= 0.5, what is the velocity of the chain when the last link leaves the
table?

E4. A flywheel of mass 100 kg and radius of gyration 20 cm is mounted
on a light horizontal axle of radius 2 cm, and is free to rotate on
bearings whose friction may be neglected. A light string wound on
the axle carries at its free end a mass of 5 kg. The system is released
from rest with the 5 kg mass hanging freely. If the string slips off
the axle after the weight has descended 2 m, prove that a couple of
moment 10/π2 kg.wt.cm. must be applied in order to bring the
flywheel to rest in 5 revolutions.
28

E5. The truss shown in the figure rotates around the pivot O in a vertical
plane at a constant angular speed ω. Four equal masses (m) hang from
the points B, C, D and E. The members of the truss are rigid,
weightless and of equal length. Find a condition on the angular speed
ω so that there is compression in the member OE.

E6. If the inputs A and B to the circuit shown below can be either 0 volts
or 5 volts,
(i) what would be the corresponding voltages at output Z, and
(ii) what operation is being performed by this circuit ?

Assume that the transistor and the diodes are ideal and base to
emitter saturation voltage = 0.5 volts.

29

E7. Two bulbs of 500 cc capacity are connected by a tube of length 20 cm
and internal radius 0.15 cm. The whole system is filled with oxygen,
the initial pressures in the bulbs before connection being 10 cm and
15 cm of Hg, respectively. Calculate the time taken for the pressures
to become 12 cm and 13 cm of Hg, respectively. Assume that the
coefficient of viscosity η of oxygen is 0.000199 cgs unit.

300 × 3.6
E8. (a) Ice in a cold storage melts at a rate of kg/hour when the
80 × 4.2
external temperature is 27oC. Find the minimum power output of
the refrigerator motor, which just prevents the ice from melting.
(Latent heat of fusion of ice = 80 cal/gm.)
(b) A vertical hollow cylinder contains an ideal gas with a 5 kg piston
placed over it. The cross-section of the cylinder is 5×10-3 m2. The
gas is heated from 300 K to 350 K and the piston rises by 0.1 m.
The piston is now clamped in this position and the gas is cooled
back to 300 K. Find the difference between the heat energy added
during heating and that released during cooling.
(1 atmospheric pressure= 105Nm-2 and g=10ms-2.)

E9. (a) A system receives 10 Kcal of heat from a reservoir to do 15 Kcal
of work. How much work must the system do to reach the initial
state by an adiabatic process?
(b) A certain volume of Helium at 15˚C is suddenly expanded to 8
times its volume. Calculate the change in temperature (assume
that the ratio of specific heats is 5/3).

E10. A spherical charge distribution has a volume density ρ, which is a
function of r, the radial distance from the center of the sphere, as
given below.
 A / r , A is constant for 0 ≤ r ≤ R
ρ= 
 0, for r > R
Determine the electric field as a function of r, for r ≥ R. Also deduce
the expression for the electrostatic potential energy U(r), given that
U(∞) = 0 in the region r ≥ R.

E11. Consider the distribution of charges as shown in the figure below.
Determine the potential and field at the point p.

30

E12. A proton of velocity 107 m/s is projected at right angles to a uniform
magnetic induction field of 0.1 w/m2. How much is the path of the
particle deflected from a straight line after it has traversed a distance
of 1 cm? How long does it take for the proton to traverse a 900 arc?

E13. (a) State the two necessary conditions under which a feedback
amplifier circuit becomes an oscillator.
(b) A two-stage FET phase shift oscillator is shown in the diagram
below.

(i) Derive an expression for the feedback factor β.
(ii) Find the frequency of oscillation.
(iii) Establish that the gain A must exceed 3.

E14. A circular disc of radius 10cm is rotated about its own axis in a
uniform magnetic field of 100 weber/m2, the magnetic field being
perpendicular to the plane of the disc. Will there be any voltage
developed across the disc? If so, then find the magnitude of this
voltage when the speed of rotation of the disc is 1200 rpm.

E15. A 3-phase, 50-Hz, 500-volt, 6-pole induction motor gives an output
of 50 HP at 900 rpm. The frictional and windage losses total 4 HP
and the stator losses amount to 5 HP. Determine the slip, rotor
copper loss, and efficiency for this load.

31

E16. A shunt D.C. generator supplies a load of two motors each drawing
46 Amps and a lighting load consisting of twenty-two 60 watt lamps
at 220V. The resistance of shunt field, series field and armature are
110 ohms, 0.06 ohms and 0.05 ohms respectively.
(i) Find the electrical efficiency of the generator.
(ii) If the overall efficiency of the generator at the above load is 77%, find
the total constant (iron and mechanical) loss.

E17. An alternator on open-circuit generates 360 V at 60 Hz when the
field current is 3.6 A. Neglecting saturation, determine the open-
circuit e.m.f. when the frequency is 40 Hz and the field-current is
24A.

E18. A single phase two-winding 20 KVA transformer has 5000 primary
and 500 secondary turns. It is converted to an autotransformer
employing additive polarity mechanism. Suppose the transformer
always operates with an input voltage of 2000 V.

(i) Calculate the percentage increase in KVA capacity.
(ii) Calculate the common current in the autotransformer.
(iii) At full load of 0.9 power factor, if the efficiency of the two-
winding transformer be 90%, what will be the efficiency of
the autotransformer at the same load ?

E19. The hybrid parameters of a p-n-p junction transistor used as an
amplifier in the common-emitter configuration are: hie = 800Ω, hfe =
46, hoe = 8 x 10-5 mho, hre = 55.4 x 10-4. If the load resistance is 5 kΩ
and the effective source resistance is 500 Ω, calculate the voltage
and current gains and the output resistance.

E20. Find the equivalent resistance between the points A and D of the
circuit shown in the diagram.

32

E21. (a) Design a special purpose counter to count from 6 to 15 using a
decade counter. Inverter gates may be used if required.
(b) For a 5 variable Boolean function the following minterms are
true: (0, 2, 3, 8, 10, 11, 16, 17, 18, 24, 25 and 26). Find a
minimized Boolean expression using Karnaugh map.

E22. In the figure, consider that FF1 and FF2 cannot be set to a desired
value by reset/preset line. The initial states of the flip-flops are
unknown. Determine a sequence of inputs (x1, x2) such that the
output is zero at the end of the sequence.

Output

33

Sample m.tech(cs)07

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