Class-XII
Physics (Theory) Time allowed: 3
Hrs Maximum Marks: 70
GENERAL INSTRUCTIONS:
1. All questions are compulsory. There are 37 questions in total.
2.
This question paper has five sections: Section A, Section B , Section C and
Section D.
3
Section A contains Questions 1 to 20 are very short answer type questions and
carry one mark each. Section B contains Questions 21 to 27 carry two marks
each, Section C question 28 to 34 carry three marks each, Section D contains questions
35 to 37 carry five marks each.
4. There is no overall choice. However an
internal choice has been provided in one question of two marks, one question
of three mark and all three questions
of five marks each. You have to attempt only one of the given choices in such
questions.
5.
Use of calculators is not permitted. However you may use log tables if
necessary.
Section A
1.
Why electric fields lines are perpendicular at a point on an
equipotential surface of a conductor?
2.
Which physical quantity is having SI units Vm? Is it a vector or
scaler?
3.
Why are alloys used for making standard resistance coils?
4.
How angle of dip vary when we move from equator towards pole of the
earth?
5.
An electron and a proton are moving along the same direction with the
same kinetic energy. When they pass through a uniform magnetic field
perpendicular to the direction of their motion, they describe paths of the same
radius. Is this statement true or false?
6.
A vertical metallic pole falls down through the plane of the magnetic
meridian. Will any emf be produced between its ends? Give reason for your
answer.
7.
A metallic piece gets hot when surrounded by a coil carrying high
frequency alternating current. Why?
8.
Name the waves, which (i) maintains the warmth and (ii) are used in
aircraft navigation.
9.
Long distance radio broadcasts use short wave bands, why?
10.
When light travel from a rarer to denser medium, the speed decreases. Does this decrease in speed imply
a decrease in the energy carried by the light wave? Justify your answer.
11.
A lens behaves as a converging lens in air and a diverging lens in
water (n=4/3). What will be the condition on the value of refractive index of
the material of the lens?
12.
Define the term stopping potential in relation to photoelectric effect.
13.
Show the variation of photocurrent with collector plate potential for
different frequencies but same intensities of incident radiation.
14.
Show graphically, the variation of the de-Broglie wavelength with the
potential through which an electron is accelerated from rest.
15.
State the Boher's quantum condition.
16.
A proton and a deuteron have same velocity, what is the ratio of their
de-Broglie wavelengths?
17.
The ground state energy of hydrogen atom is -13.6 eV. What are the
kinetic and potential energies of the electron in this state?
18.
When an electron falls from a higher energy to a lower energy level,
the difference in the energies appears in the form of em radiation. Why cannot
it be emitted as other forms of energy?
19.
Explain why elemental semiconductor cannot be used to make visible
LEDs.
20.
What do you mean by fermi level?
Section
B
21.
Establish a relation between intensity of electric field and potential
gradient.
OR
A point charge q is placed at point O is shown
in fig. Is Vᵖ - VQ positive or negative when
Justify your answer.
22.
Define Self-inductance of a coil. Show that magnetic energy required
building up the current I in a coil of self-inductance L is given by ½ LI2
23.
In young’s experiment, the width of the fringes obtained with the light
of wavelength 6000Aᵒ is 2 mm in air. What will be the fringe width if the
entire apparatus is immersed in water of refractive index 4/3?
24.
Using a labeled circuit diagram, explain the working of a full wave
rectifier using p-n junction diodes.
25.
The amplitude of the magnetic field of a harmonic em wave in vacuum is
B0=510nT. What is the amplitude of the electric field part of the
wave?
26.
Find the wavelength of em waves of frequency 6X1012 Hz in
free space. Give its two applications.
27.
State laws of photo electric emission.
Section C
28.
Find the torque experienced by
an electric dipole in uniform external electric field placed at certain angle.
Also explain stable and unstable equilibrium.
29.
(i)
State Kirchhoff’s rules.
(ii) Explain with the help of a circuit diagram; how the value of unknown
resistance can be determine using a slide wire bridge.
OR
Define the current density. Establish a
relation between current density, electric field and conductivity.
30.
Write the expression for the force per unit between two infinitely long
parallel straight current carrying conductors. Hence define the SI unit of
current?
31.
A conducting rod of length
with one end pivoted is rotated
with uniform angular velocity
in a vertical plane, normal to a
uniform magnetic field B. Deduce an expression for emf induced in this rod?
32.
What does a Polaroid consist of? Show using a simple Polaroid, that
light waves are transverse in nature. Intensity of light coming out of a
Polaroid does not change irrespective of the orientation of the pass axis of
the Polaroid. Explain why.
33.
The binding energy per nucleon of deuteron (1H2)
and helium nucleus (2He4 ) is known to be 1.1 MeV
and 7 MeV respectively. If
two deuteron nuclei react to
form a single
helium nucleus; calculate the energy released?
34.
Explain the forward and reverse biasing of a p-n junction diode. Also
draw the characteristics of forward and reverse biasing.
Section D
35.
(i) State Gauss theorem in electrostatics. Using it, find a
relation for the Electric Field at a point due to infinite sheet of charge.
(ii) A capacitor of 10 µF is charged to 20 volt and
disconnected from the source and then combined across an identical uncharged
capacitor. Find the common potential and the loss of energy in this process.
OR
Establish a relation for
Electric Field Intensity at an axial point of an electric dipole using a proper
diagram.
An electric dipole of
dipole moment 5X10-20 Cm is kept in a uniform electric field of
intensity 104 NC-1 making an angle of 30ᵒ with direction
of Electric field. Find the torque on the dipole.
36.
(i) Draw a labeled ray diagram of a compound microscope. Write down
a relation for its magnifying power.
(ii)The length of tube of
telescope in normal adjustment is 101 cm and its magnifying power is 100. Find
the focal length of objective and eye piece of the telescope.
OR
(a)What is single slit
experiment of diffraction? Discuss the position of minima and hence find the
relation for width of central maxima.
(b) Write down the
relation for resolving power of microscope. What is the effect on resolving
power if the microscope is immersed in water?
26. With the help of a
labelled diagram explain the working principle and theory of a step down
transformer. Why a transformer is not used to step up or down the dc voltage.
OR
(a)
With the help of a phasor diagram find the impedance of a LCR circuit.
Also explain resonance condition of the circuit.
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