Board Paper of Class 12-Science 2010 Physics (SET 3) - Solutions
General Instructions:
(i) All questions are compulsory.
(ii) There are 30 questions in total. Question Nos. 1 to 8 are very short answer type questions and carry one mark each.
(iii) Question Nos. 9 to 18 carry two marks each, question 19 to 27 carry three marks each and question 28 to 30 carry five marks each.
(iii) There is no overall choice. However, an internal choice has been provided in one question of two marks; one question of three marks and all three questions of five marks each. You have to attempt only one of the choice in such questions.
(iv) Use of calculators is not permitted.
- Question 1
A plot of
magnetic flux (Φ) versus current (I) is shown in the figure
for two inductors A and Β. Which of the two has larger value of
self inductance?
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- Question 2
Figure
shows three point charges +2q, −q and + 3q. Two charges + 2q
and −q are enclosed within a surface ‘S’. What is
the electric flux due to this configuration through the surface ‘S’?
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- Question 3
In which orientation, a dipole placed in a uniform electric field is
in (i) stable, (ii) unstable equilibrium?
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- Question 4
Which part of electromagnetic spectrum is used in radar systems?
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- Question 5
Calculate the speed of light in a medium whose critical angle is 30°.
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- Question 6
A glass
lens of refractive index 1.45 disappears when immersed in a liquid.
What is the value of refractive index of the liquid?
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- Question 7
Write the expression for Bohr’s radius in hydrogen atom.
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- Question 8
A wire of
resistance 8R is bent in the form of a circle. What is the effective
resistance between the ends of a diameter AB?
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- Question 9
Explain the function of a repeater in a communication system.
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- Question 10
(i) Write two characteristics of a material used for making permanent magnets.
(ii) Why is the core of an electromagnet made of ferromagnetic materials?
OR
Draw magnetic field line when a (i) diamagnetic, (ii) paramagnetic substance is placed in an external magnetic field. Which magnetic property distinguishes this behaviour of the field line due to the substances?
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- Question 11
What is
the range of frequencies used in satellite communication? What is
common between these waves and light waves?
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- Question 12
A coil Q
is connected to low voltage bulb B and placed near another coil P as
shown in the figure. Give reasons to explain the following
observations:
(a) The bulb ‘B’ lights
(b) Bulb gets dimmer if the coil Q is moved towards left.
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- Question 13
Find the
radius of curvature of the convex surface of a plano-convex lens,
whose focal length is 0.3 m and the refractive index of the material
of the lens is 1.5.
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- Question 14
An
electron is accelerated through a potential difference of 64 volts.
What is the de-Broglie wavelength associated with it? To which part
of the electromagnetic spectrum does this value of wavelength
correspond?
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- Question 15
(i) Out of blue and red light which is deviated more by a prism? Give
reason.
(ii) Give the formula that can be used to determine refractive index
of materials of a prism in minimum deviation condition.
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- Question 16
Plot a
graph showing the variation of stopping potential with the frequency
of incident radiation for two different photosensitive materials
having work functions W1 and W2 (W1
> W2). On what factors does the (i) slope and (ii)
intercept of the lines depend?
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- Question 17
Draw the circuit diagram of an illuminated photodiode in reverse bias. How is photodiode used to measure light intensity?
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- Question 18
A heavy nucleus X of mass number 240 and binding energy per nucleon 7.6 MeV is split into two fragments Y and Z of mass numbers 110 and 130. The binding energy of nucleons in Y and Z is 8.5 MeV per nucleon. Calculate the energy Q released per fission in MeV.
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- Question 19
(a) Depict the equipotential surfaces for a system of two identical
positive point charges placed a distance ‘d’ apart.
(b) Deduce the expression for the potential energy of a system of two
point charges q1 and q2 brought from infinity
to the points
and
respectively
in the presence of external electric field
.
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- Question 20
In a meter
bridge, the null point is found at a distance of l1
cm from A. If now a resistance of X is connected in parallel with S,
the null point occurs at l2 cm. Obtain a formula
for X in terms of l1, l2 and S.
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- Question 21
What is
space wave propagation? Give two examples of communication system
which use space wave mode.
A TV tower is 80 m tall. Calculate the
maximum distance upto which the signal transmitted from the tower can
be received.
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- Question 22
(i) Define ‘activity’ of a radioactive material and write
its S.I. units.
(ii) Plot a graph showing variation of activity of a given
radioactive sample with time.
(iii) The sequence of stepwise decay of a radioactive nucleus is
If the atomic number and mass number of D2 are 71 and 176
respectively, what are their corresponding values of D?
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- Question 23
What is an
unpolarized light? Explain with the help of suitable ray diagram how
an unpolarized light can be polarized by reflection from a
transparent medium. Write the expression for Brewster angle in terms
of the refractive index of denser medium.
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- Question 24
Write the
principle of working of a potentiometer. Describe briefly, with the
help of a circuit diagram, how a potentiometer is used to determine
the internal resistance of a given cell.
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- Question 25
Write the
expression for the magnetic moment
due
to a planar square loop of side ‘l’ carrying a
steady current I in a vector form.
In the
given figure this loop is placed in a horizontal plane near a long
straight conductor carrying a steady current I1 at a
distance l as shown. Give reason to explain that the loop will
experience a net force but no torque. Write the expression for this
force acting on the loop.
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- Question 26
A long
straight wire of a circular cross-section of radius ‘a’
carries a steady current ‘I’. The current is uniformly
distributed across the cross-section. Apply Ampere’s circuital
law to calculate the magnetic field at a point ‘r’ in the
region for (i) r < a and (ii) r > a.
OR
State the
underlying principle of working of a moving coil galvanometer. Write
two reasons why a galvanometer can not be used as such to measure
current in a given circuit. Name any two factors on which the current
sensitivity of a galvanometer depends.
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- Question 27
A
parallel-plate capacitor is charged to a potential difference V by a
dc source. The capacitor is then disconnected from the source. If the
distance between the plates is doubled, state with reason how the
following change:
(i) electric field between the plates
(ii) capacitance, and
(iii) energy stored in the capacitor
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- Question 28
(a) Explain the formation of depletion layer and potential barrier in
a p−n junction.
(b) In the figure given below the input waveform is converted into
the output waveform by a device ‘X’. Name the device and
draw its circuit diagram.
(c) Identify the logic gate represented by the circuit as shown and
write its truth table.
OR
(a) With the help of circuit diagram explain the working principle of
a transistor amplifier as an oscillator.
(b) Distinguish between a conductor, a semiconductor and an insulator
on the basis of energy band diagrams.
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- Question 29
Describe
briefly, with the help of a labelled diagram, the basic elements of
an A.C. generator. State its underlying principle. Show
diagrammatically how an alternating emf is generated by a loop of
wire rotating in a magnetic field. Write the expression for the
instantaneous value of the emf induced in the rotating loop.
OR
A series
LCR circuit is connected to a source having voltage v = vm
sin ωt. Derive the expression for the instantaneous current I
and its phase relationship to the applied voltage.
Obtain the
condition for resonance to occur. Define ‘power factor’.
State the conditions under which it is (i) maximum and (ii) minimum.
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- Question 30
State
Huygens’s principle. Show, with the help of a suitable diagram,
how this principle is used to obtain the diffraction pattern by a
single slit.
Draw a
plot of intensity distribution and explain clearly why the secondary
maxima becomes weaker with increasing order (n) of the secondary
maxima.
OR
Draw a ray
diagram to show the working of a compound microscope. Deduce an
expression for the total magnification when the final image is formed
at the near point.
In a
compound microscope, an object is placed at a distance of 1.5 cm from
the objective of focal length 1.25 cm. If the eye piece has a focal
length of 5 cm and the final image is formed at the near point,
estimate the magnifying power of the microscope.
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