PHYSICS
Time: ONE Hour 
Max. Marks: 50 
·
Answers
must be written either in English or
the medium of instruction of the candidate in high school.
·
Answer
all the questions in the booklets
provided for the purpose.
·
There
will be no negative marking.
·
The relevant
working or the argument in arriving at an answer has to be included in your answer.
·
Use
of calculators is not permitted.
·
Questions
in Part A carry 5 marks
each , questions in part B carry 3 marks
each, questions in part
C carry 5 marks.
Part
A
1. A solid sphere and a hollow
sphere of same external radius and made of same material are floating
in water.
Solid sphere has three fourths of its volume submerged and the hollow
sphere is
half submerged. What fraction of the volume of hollow sphere is hollow?
2. Two men are running on a
circular track. They start from the same position. If they take
3 minutes
and 5 minutes to run once around the track, find the time interval
between successive
crossings and the number of times they cross each other in an hour if
they
travel the path in (i) opposite sense (ii) same sense
3. A lens of focal length 20 cm
forms the image of a bright object kept 30 cm from it on a screen. If
the lens
is replaced by another lens, the object has to be moved by 5 cm to
obtain a
sharp image on the screen. Find the possible values of the focal length
of the
second lens.
4. A wire of resistance R is bent to form a ring.
Contacts can be made at points A and B on the ring. A is a fixed
contact and B can not be closer to A than a quarter of the perimeter of
the ring. Find the maximum and minimum possible resistances between
various choices of the contact point B.


5. A rowboat travels
downstream on a river at a speed of 8 m/s with respect to the
shore. A
motorboat comes from the opposite direction at a speed of
10 m/s with
respect to the water. 10 seconds after meeting each other they are at
160
metres from each other. At what speed does the river flow
6. A piece of ice at10 ^{o}C
is heated to 1 ^{o}C using a certain
quantity of energy. Then
another 20 times as much energy is necessary to finally obtain water.
Using
that the specific heat of ice is half of the specific heat of
4.2 kJ/(kg ^{o}C) of water,
determine the heat of fusion of
ice from the above measurement data.
Part
B
7. The electrical power of a
vacuum cleaner is 1 kW. It expels 50 litre of air per
second with a
speed of 80 m/s. What percent of the total power is in the
form of kinetic
energy of air? (Density of
the flowing air is 1.2 ´ 10^{3}
gcm^{3})
8. A stone is projected
vertically upward from some height at 2v. Some Dt later another stone is
projected vertically upward at v from the same position. If they reach
the
initial position at the same time, find v.
9. A nuclear reactor uses 1 kg
of uranium enriched to 1% in one hour. Assuming 60% efficiency find the
electrical power generated. Assume each fission of uranium nucleus
produces 200
MeV of energy and 238 g of Uranium contains 6.0´10^{23} atoms. What
fraction of mass has disappeared in the process?
10. An alpha particle moving vertically
downward at right angles to a uniform magnetic field experiences a
northward
force. What is the direction of the force on a beta particle moving
northward?
11. A ray of light is incident at E at 45° as it passes from air in to a medium across
boundary AB. It then is incident at F on boundary CD and emerges in to
air. Sum of the angles at E and F in the medium is 60°. Find the deviation of the ray at F.
Refractive index of the medium with respect to air is Ö2.


Part
C
12. Nucleons in a nucleus are
held together by attractive short range forces. These forces are
stronger than
columbic forces and act between neighbouring nucleons. These forces are
charge
independent.
Explain in one are two sentences why
(i) A large nucleus can not consist only of protons
(ii) All matter is not
nuclear.
(2
Marks)
13. X
rays are produced when a
beam of electrons strikes a target. If n electrons strike the target in
one
second, find (i) the beam current in an x ray tube. If electrons are
accelerated by V before striking the target, find the rate at which
heat is
produced in the target if 90% of their kinetic energy is converted to
heat.
(3
Marks)
