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First Year/ First Semester
Subject: Physics I
FM: 60
Time: 3 hours
PM: 24
Candidates are required to give their answers in their own words
as far as practicable. The figures in the margin indicate full marks.
Year: 2065
Section A
Long Answer Questions
Answer any four:
1.
What is meant by Galilean
invariance? Show that distance and acceleration are invariant to Galilean
transformation, velocity is not invariant. (2+1.5+1.5+2)
2.
It is given that the potential energy of a system is
rotationally invariant. What do you mean by rotational invariance? Show that angular momentum is conserved for such a system.
(3.5+3.5)
3.
(a) Discuss the analogy between liquid-flow and current-flow and hence, derive an expression for liquid-flow through capillaries in series. (4)
(b) State Gauss’s law and use it
to show that excess charge of a
charged conductor resides on its outer surface. (3)
4.
(a) Discuss the analogy between liquid-flow and current-flow and hence, derive an expression for liquid-flow through capillaries in series. (4)
(b) State Gauss’s law and use it
to show that excess charge of a
charged conductor resides on its outer surface. (3)
5.
Derive the expression for energy
density in the magnetic field. (7)
6.
Explain the empirical basis for writing
the Maxwell’s equations and write them. (7)
Section B
Short Answer
Questions
Answer any eight:
7.
A proton is accelerated through a potential difference 50V and then it
is allowed cross a field free region 7.5m
long. Find the time required to cross this distance. (4)
8.
Find the height of geostationary
satellite (as viewed by an observer on the
earth’s surface); given g=9.8 ms-2on the earth’s surface, R=
6.38 x 105m. (4)
9.
The potential
energy for the Vander Waals force between
two atoms is given by
, where x is the distance between the two
atoms and a and b are positive constants. Calculate the force between two atoms
and plot it against x. (4)
10. A parallel LCR circuit has L= 8mH, C= 10 µF and
R= 0,5Ω. Calculate the natural frequency and
quality factor. (4)
11. A water drop of radius 0.01 mm is falling through air
neglecting the density of air as compared
to the water, calculate the terminal
velocity of the drop ( ɳ
for air
= 1.8 x 10-4 CGS units) (4)
12.
Two point charges of and - 
are
located at the origin and at (a, 0, 0)
respectively.
are
located at the origin and at (a, 0, 0)
respectively.
Find the point where electric field vanishes. (4)
13. Two parallel conducting plates are separated by the
distance d and potential difference ᐃψ. A
dielectric slab of dielectric
constant k is and of uniform thickness
is tightly
fitted between the plates. Find the electric
field in the dielectric. (4)
14. What is the capacitance of a capacitor that can store 800 J at 800 V? Suppose the capacitor has
parallel plates separated by 10-5 m and filed with a dielectric of dielectric
constant 2.2. What is the area of
the plates? (4)
15. Consider a simple RL circuit
in which a sudden voltage V is
applied. Discuss its transient behavior and find the current as a function of time.
|
Show
that the time average power dissipation in a circuit which carries an AC current 
and 
is . Here z is the impedance of the circuit: (4)
and is . Here z is the impedance of the circuit: (4)
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