PRE MOCK PRACTICE PAPER-2
ISC 12
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Maximum Marks: 70
Time Allowed: Three Hours
(Candidates are allowed additional 15 minutes for only reading the paper.
They must NOT start writing during this time.)
This paper is divided into four sections – A, B, C and D.
Answer all questions.
Section A consists of one question having sub-parts of one mark each.
Section B consists of seven questions of two marks each.
Section C consists of nine questions of three marks each, and
Section D consists of three questions of five marks each.
Internal choices have been provided in two questions each in Section B,
Section C and Section D.
The intended marks for questions are given in brackets [ ].
All working, including rough work, should be done on the same sheet as and adjacent to the rest
of the answer.
Answers to sub parts of the same question must be given in one place only. A list of useful
physical constants is given at the end of this paper.
A simple scientific calculator without a programmable memory may be used for calculations.
Section A – 14 Marks
Q.1. (A) Multiple Choice Questions [7
Marks]
(i) In charging by induction,
(a) body to be charged must be an insulator
(b) body to be charged must be a semiconductor
(c) body to be charged must be a conductor
(d) any type of body can be charged by induction
(ii) In diffraction from a single slit the angular width of the central maxima does not depend on
(a) λ of light used (c) distance of slits from the screen
(b) width of slit D
(d) ratio of λ and slit width
(iii) Assertion The focal length of the mirror is ƒ and distance of the object from the focus is u.
The magnification of the mirror is flu.
¿ image
Reason Magnification =
¿ object
(a) Both Assertion and Reason are correct and Reason is the correct explanation of
Assertion.
(b) Both Assertion and Reason are correct but Reason is not the correct explanation of
Assertion.
(c) Assertion is correct but Reason is incorrect.
(d) Assertion is incorrect but Reason is correct.
(iv) Which of the following is not a unit of electrostatic potential?
(a) Volt (c) Newton/Coulomb
(b) Joule/Coulomb (d) Newton-Metre/Coulomb
(v) Light waves travel in vacuum along the Y-axis. Which of the following may represent the
wavefront?
(a) y = constant (c) z = constant
(b) x = constant (d) x + y + z = constant
(vi) Einstein's photoelectric equation is
(a) Emax =hλ−ϕ0 (c) Emax =h v+ ϕ 0
hc hc
(b) Emax = −ϕ 0 (d) Emax = + ϕ 0
λ λ
(vii) If the orbital radius of the electron in a hydrogen atom is 4.7 × 10 -11 m. Compute the kinetic
energy of the electron in hydrogen atom.
(a) 15.3 eV (c) 13.6 eV
(b) - 15.3 eV (d) -13.6 eV
Q.1. (B) Answer the following questions [7 Marks]
(i) Explain the statement "Light added to light can produce darkness".
(ii) A small telescope has an objective lens of focal length 144 cm and an eyepiece of focal
length 6.0 cm. What is the magnifying power and length of the tube of this telescope?
(iii) Name the type of a diode whose characteristics are shown below
(iv) Is the ratio of number of holes and the number of conduction electrons in an n-type
extrinsic semiconductor is more than, less than or equal to 1?
(v) Name the series of lines in the hydrogen spectrum which lie in the visible region.
(vi) What is the SI unit of magnetic field in terms of N, A and m? State whether magnetic field
is scalar or vector quantity.
(vii) The direction of ray of light incident on a concave mirror is shown by PQ while directions
in which the ray would travel after reflection is shown by four rays marked as 1, 2, 3 and 4
in the figure? Which of the four rays correctly shows the direction of reflected rays?
SECTION B – 14 MARKS
Question 2 [2]
Give four conclusions of de-Broglie equations.
OR
Show graphically the effect of intensity of light on photoelectric current.
Question 3 [2]
(i) In an electromagnetic wave, how are electric field vector (E), magnetic field vector (B) and
velocity of propagation of the wave (c) oriented?
(ii) How much time would gamma radiation take to travel from the sun to the earth, a distance
of 1.5x10¹¹ m?
Question 4 [2]
What is the nuclear radius of ¹²⁵Fe, if that of ²⁷Al is 6.4 fermi?
Question 5 [2]
(i) Write the expression for equivalent focal length of two thin convex lenses placed in contact
with each other.
(ii) What is the magnification of combination given in part (i)?
Question 6 [2]
In Young's double slit experiment, using monochromatic light of wavelength 700 nm. The interference
pattern was obtained on a screen kept 1.5 m away from the plane of two slits. Calculate the distance
between the two slits, if the fringe separation or width was found to be 1.0 mm.
Question 7 [2]
Mention any two properties of an L-C-R circuit at resonance.
Question 8 [2]
An element ∆l = ∆x î is placed at the origin (as shown in figure) and carries a current I = 2A Find out
the magnetic field at a point P on the Y-axis at a distance of 1.0 m due to the element ∆x = w cm. Also,
give the direction of the field produced.
OR
Two long wires carrying currents I1 and I2 are arranged as shown in the figure. One carrying current I 1
along the X-axis. The other carrying current I 2 along a line parallel to Y-axis, given by x = 0 and z = d.
Find the force exerted at point O₂ because of the wire along the X-axis.
SECTION C – 27 MARKS
Question 9 [3]
Prove the law of reflection of light on the basis of Huygens' wave theory of light.
ОR
(i) A man with normal near point (25 cm) reads a book with small print using a magnifying
glass: a thin convex lens of focal length 5 cm. What is the closest and the farthest distance
at which he should keep the lens from the page, so that he can read the book when viewing
through the magnifying glass?
(ii) Draw a labelled diagram of simple microscope at normal adjustment.
Question 10 [3]
Figure shows two identical capacitors C₁ and C 2 each of 2 µF capacitance, connected to a battery of 5
V. Initially switch S is left open and dielectric slabs of dielectric constant X = 5 are inserted to fill
completely the space between the plates of the two capacitors. How will the charge and potential
difference between the plates of the capacitors be affected after the slabs are inserted?
Question 11 [3]
(i) Define Gauss' law.
(ii) A thin straight infinitely long conducting wire having charge density λ is enclosed by a
cylindrical surface of radius r and length I, its axis coinciding with the length of the wire.
Find the expression for the electric flux through the surface of the cylinder.
Question 12 [3]
Magnetic field lines are a visual and intuitive realization of the magnetic field. These are those
imaginary lines which continuously represent the direction of the magnetic field.
They are in the form of closed loops. Field lines for a bar magnet are as shown in figure below
Now, with the help of above information,
(i) sketch magnetic field lines around a current carrying finite solenoid
(ii) how is the direction of a magnetic field line represented?
(iii) does these lines resemble to the electric field lines of an electric dipole?
OR
(i) How does a circular loop carrying current behave as a magnet?
(ii) On what factors does the pole strength of a magnet depend?
Question 13 [3]
(i) With reference to an electric cell, define
(a) electromotive force (emf) of a cell and
(b) internal resistance (r).
(ii) A cell of emf E and internal resistance r is connected across a variable resistor R. Plot a
graph showing the variation of terminal potential V with resistance R.
Question 14 [3]
Study the circuits (a) and (b) shown in the figure and answer the following questions:
(i) Under which conditions would the rms currents in the two circuits be the same?
(ii) Can the rms current in circuit (b) be larger than that in (a)?
Question 15 [3]
In the fusion reaction,
1H + 1H → 2He + 0n the masses of deuteron, helium and neutron expressed in amu are 2.015, 3.017
2 2 3 1
and 1.009, respectively. If 1kg of deuterium undergoes complete fusion, then find the amount of total
energy released. (Take. 1 amu = 931.5 MeV/c²)
Question 16 [3]
Can de-Broglie hypothesis be used to comment on Bohr's second postulate? If yes, then state the
hypothesis and use it to make inferences about Bohr's postulate.
Question 17 [3]
An experiment on potentiometer is performed by a student. The examiner gives the following
instruction to student. State whether the responses of student are correct or not.
(i) EXAMINER The potential gradient along the potentiometer wire is too low. Increase its
value.
STUDENT increases the length of the potentiometer wire used (thinking that increasing
the length will increase the potential gradient).
(i) EXAMINER The emf of the unknown cell is not very high. Increase its value.
STUDENT connects additional cells in series with the unknown cell to increase the
total emf.
(ii) EXAMINER The potentiometer wire is too short to measure high potential difference
accurately. Increase the effective length of the potentiometer wire.
STUDENT Add a long resistance wire in series with the existing potentiometer wire.
SECTION D – 15 MARKS
Question 18 [5]
(i) A sinusoidal voltage of peak value 283 V and frequency 50 Hz is applied to a series L-C-R
circuit in which R = 3 Ω, L = 25.48 mH and C = 796 µF. Find
(a) the impedance of the circuit.
(b) the phase difference between the voltage across the source and the current.
(c) the power factor.
(ii) Prove mathematically that the average value of alternating current over one complete cycle
is zero.
OR
(i) Two concentric circular coils, one of small radius and the other of large radius r 2 such that r1
<< r2 are placed coaxially with centres coinciding. Obtain the mutual inductance of the
arrangement.
(ii) State Lenz's law. A metallic rod held horizontally along East-West direction, is allowed to
fall under gravity. Will there be an emf induced at its ends? Justify your answer.
(iii) State the conditions in which magnetic flux linked with a coil is
(a) maximum
(b) minimum
Question 19 [5]
(i) When the width of the slit is made double, how would this affect the size and intensity of
the central diffraction band? Justify your answer.
(ii) The intensity at the central maxima (O) in a Young's double slit experiment is I o. If the
distance OP equals two-third of fringe width of the pattern, show that the intensity at point
P would be Io/4.
OR
(i) A lens whose radii of curvature are different is forming the image of an object on its axis.
Will the position of image change, if the lens is placed with its faces reversed?
(ii) What happens to a focal length of a convex lens, when it is immersed in water?
(iii) The radii of curvature of the surfaces of a double convex lens are 20 cm and 40 cm,
respectively and its focal length is 20 cm. What is refractive index of the material of the
lens?
Question 20 [5]
Read the passage given below and answer the questions that follow.
Full Wave Rectifier
The process of converting alternating voltage/current into direct voltage/current is called rectification.
Diode is used as a rectifier for converting alternating current/voltage into direct current/voltage.
Diode allows current to pass only when it is forward biased. So, if an alternating voltage is applied
across a diode, the current flows only in that part of the cycle when the diode is forward biased. This
property is used to rectify the current/voltage.
(i) In the following diode circuit, input is given between terminals A and C and output is taken
between terminals B and D. What is the nature of output voltage?
(ii) For what purpose, rectifier is used?
(iii) In the following circuit diagram, what is the use of capacitor C?
