Practice Test Paper 1
Physics
(Theory) – XII
Time
allowed: 3 hours Maximum
marks: 70
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Q. 1.
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An
electric dipole of dipole moment 20x10-6 C.m is enclosed by a
closed surface. What is the net flux coming out of the surface?
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1
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Q. 2.
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A bulb
and a capacitor are connected in series to an a.c. source of variable
frequency. How will the brightness of the bulb change on increasing the
frequency of the a.c. source? Give reason.
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1
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Q. 3.
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Write
one condition under which an electric charge does not experience a force in a
magnetic field.
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1
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Q. 4.
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Name
the type of biasing of a p-n junction diode so that the junction offers very
high resistance.
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1
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Q. 5.
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What
should be the length of the dipole antenna for a carrier wave of frequency
3x108 Hz?
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1
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Q. 6.
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Draw V-I graph for ohmic and non-ohmic materials. Give one
example for each.
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2
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Q. 7.
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How
does the resistivity of (a) a conductor and (b) a semiconductor vary with
temperature? Give reason for each case.
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2
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Q. 8.
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State
the condition under which the phenomenon of resonance occurs in a series LCR
circuit. Plot a graph showing variation of current with frequency of a.c.
source in a series LCR circuit.
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2
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Q. 9.
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Explain
the term (a) pulse-amplitude modulation (PAM) and (b) pulse-code modulation
(PCM).
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2
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Q. 10.
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An
electron and a proton have the same kinetic energy. Which of the two has a
greater wavelength? Explain.
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2
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Q. 11.
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Explain,
with the help of a circuit diagram, how the thickness of depletion layer in a
p-n junction diode changes when it is forward biased.
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2
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Q. 12.
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An
electron and a proton are moving in the same direction and possess same
kinetic energy. Find the ratio of de Broglie wavelengths associated with
these particles.
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2
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Q. 13.
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Define
the term ‘resistivity’ and write its S.I. unit. Derive the expression for the
resistivity of a conductor in terms of number density of free electrons and
relaxation time.
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3
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Q. 14.
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A figure divided into squares, each of size 1 mm2
is being viewed at a distance of 9 cm through a magnifying lens of focal
length 10 cm, held close to the eye.
(a) Draw
a ray diagram showing the formation of the image.
(b) What
is the magnification produced by the lens? How much is the area of each
square in the virtual image?
What
is the angular magnification of the lens?
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3
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Q. 15.
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Two cells of emf 1.5 V and 2 V and internal resistance 1
ohm and 2 ohm respectively are connected in parallel to pass a current in the
same direction through an external resistance of 5 ohm.
(a) Draw
the circuit diagram.
Using
Kirchhoff’s laws, calculate the current through each branch of the circuit
and potential difference across the 5 ohm resistor.
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3
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Q. 16.
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Deduce
an expression for the capacitance of a parallel plate capacitor with air as
the medium between the plates.
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3
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Q. 17.
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Define
the term ‘resistivity’ and ‘conductivity’ and state their S.I. units. Draw a
graph showing the variation of resistivity with temperature for a typical
semiconductor.
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3
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Q. 18.
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A
system has two charges qA = 2.5x10-7 C and qB
=-2.5x10-7 C located at points A (0,0,-15cm) and B(0,0,+15cm)
respectively. Calculate the electric dipole moment of the system. What is its
direction?
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3
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Q. 19.
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How
will a dia-, para- and a ferro-magnetic material behave when kept in a
non-uniform external magnetic field? Give one example of each of these
materials.
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3
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Q. 20.
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The sequence of stepwise decays of a radioactive nucleus
is
D
 D1  D2 D3
If the
nucleon number and atomic number for D2 are 176 and 71
respectively, what are the corresponding values of D and D3?
Justify your answer in each case.
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3
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Q. 21.
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Name the radiations of electromagnetic spectrum which are
used in
(a) Warfare
to look through fog.
(b) Radar
and geostationary satellites.
(c) Studying
the structure and properties of atoms and molecules.
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3
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Q. 22.
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What
is an optical fibre? Explain with the help of a diagram, how light can travel
through it and remain confined to the fibre.
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3
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Q. 23.
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A
radioactive sample contains 2.2 mg of pure
 , which has half-life period of 1224 seconds. Calculate (a)
the number of atoms present initially, and (b) the activity when 5 mg
of the sample will be left. |
3
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Q. 24.
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Draw a
schematic diagram of a single optical fibre structure. Explain briefly how an
optical fibre is fabricated. Describe in brief, the mechanism of propagation
of light signal through an optical fibre.
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3
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Q. 25.
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Define the term electric field intensity. Write its SI
unit. Derive an expression for the electric field intensity at a point on the
axis of an electric dipole.
Or
State
Gauss theorem in electrostatics. Use it to obtain an expression for the
electric field intensity at a point near a uniformly charged infinite plate
sheet.
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5
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Q. 26.
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Draw a labelled diagram of a compound microscope when
the image is formed at infinity. Deduce the expression for its magnifying
power. How can the magnifying power be increased?
Or
Draw a
labelled diagram to show the image formation in an astronomical telescope.
Write an expression for its magnifying power.
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5
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Q. 27.
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(a) Distinguish between metals, insulators and
semiconductors on the basis of their energy bands.
(b) A semiconductor has equal electron and hole concentration
of 6x108 /m3. On doping with certain impurity, electron
concentration increases to 9x1012/m3.
(i)
Identify the new semiconductor obtained after doping
(ii)
Calculate the new hole concentration
Or
(a) Draw
a circuit diagram of a p-n-p transistor as an amplifier in a common emitter
configuration.
(b) Calculate
the voltage gain for a transistor having a current gain 40, collector
resistance 6 kilo-ohm and input resistance 1 kilo-ohm.
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5
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