अनुक्रम ांक/ROLL NO सेट / SET: 3
केंद्रीय विद्यालय संगठन ,जयपरु संभाग
KENDRIYA VIDYALAYA SANGATHAN, JAIPUR REGION
PRACTICE EXAM :2024-25
कक्षा / CLASS: XII
विषय /SUB: PHYSICS (कोड / CODE:042)
अधिकतम आवधि / Time Allowed: 3 Hours अधिकतम अांक / Maximum Marks: 70
स म न्य धनर्दे श / General Instructions:
(1) There are 33 questions in all. All questions are compulsory.
(2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E.
(3) All the sections are compulsory.
(4) Section A contains sixteen questions, twelve MCQ and four Assertion Reasoning based questions of 1
mark each, Section B contains five questions of two marks each, Section C contains seven questions
of three marks each, Section D contains two case study-based questions of four marks each and
Section E contains three long answer questions of five marks each.
(5) There is no overall choice. However, an internal choice has been provided in one question in Section
B, one question in Section C, one question in each CBQ in Section D and all three questions in Section
E. You have to attempt only one of the choices in such questions.
(6) Use of calculators is not allowed.
(7) You may use the following values of physical constants where ever necessary
a. C = 3 x108 m/s
b. Me = 9.1x10-31 kg
c. Mp = 1.7x10-27 kg
d. e = 1.6x10-19 C
e. µ0 = 4πx10-7 Tm𝑨−𝟏
f. h = 6.63 x10-34 Js
g. ε0 = 8.854 x10-12 𝑪𝟐𝑵−𝟏𝒎−𝟐
h. Avogadro’s number = 6.023X𝟏𝟎𝟐𝟑 per gram mole
Q.N. [Section – A] Marks
Q.1 A uniform electric field pointing in positive X-direction exists in a region. Let A be the origin, 1
B be the point on the X-axis at x = +1 cm and C be the point on the Y-axis at y = +1 cm. Then
the potential at points A, B and C are VA,VB and VC satisfy
(A) VA< VB (B) VA > VB. (C) VA < VC (D) VA > VC
Q.2 Electric field intensity at a point in between two parallel sheets with like charges of same 1
surface charge densities (σ) is
𝜎 3𝜎 2𝜎
(a) 2𝜖 (b) 𝜖 (c) 𝜖 (d) Zero
𝑜 𝑜 𝑜
Q.3 A long straight wire of circular cross section of radius ҅a᾿ carries a steady current I. The 1
current is uniformly distributed across its cross section. The ratio of magnitudes of the
magnetic field at a point a/2 above the surface of wire to that of a point a/2 below its
surface is
(A) 4:1 (B) 1:1 (C) 4: 3 (D) 3 :4
1
Q.4 Half of the lens is wrapped in black paper. How will it change the image 1
(A)Size of image is halved
(B)Intensity of image is reduced
(C)There is no change in the size of image or intensity
(D)Both size and intensity of the image are changed
Q.5 An electric dipole is placed at an angle of 30º to a non-uniform electric field. The dipole will 1
experience
(A) a torque only
(B) a translation force only in the direction of the field
(C) a translation force only in a direction normal to the direction of the field
(D) a torque as well as a translation force
Q.6 In a series LCR circuit, the voltage across the resistance, capacitance and inductance is 10 V 1
each. If the capacitance is short circuited the voltage across the inductance will be
(A) 10 V (B) 10√2 V (C) 10/√2 V (D) 20 V
Q.7 In electromagnetic waves the phase difference between electric and magnetic field vectors 1
are
(A) Zero ( B) 𝜋/4 (C) 𝜋/2 (D) π
Q.8 The distance of closest approach of an alpha particle is d when it moves with a speed V 1
towards a nucleus. Another alpha particle is projected with higher energy such that the new
distance of the closest approach is d/2. What is the speed of projection of the alpha particle
in this case?
(A) V /2 (B) √2 V (C) 2 V (D) 4 V
Q.9 In a Young’s double slit experiment, the path difference at a certain point on the screen 1
between two interfering waves is 1/8th of the wavelength. The ratio of intensity at this point
to that at the Centre of a bright fringe is close to
(a) 0.80 (b) 0.74 (c) 0.94 (d) 0.85
Q.10 In optical fibres, propagation of light is due to 1
(A) Diffraction (B) total internal reflection (C) reflection (D) refraction.
Q.11 Ratio of the radii of the nuclei with mass numbers 8 and 27 would be 1
27 8 2 3
(A) (B) (C) (D)
8 27 3 2
Q.12 Two wire of the same material have lengths l and 2l and areas of cross section 4A and A 1
respectively. The ratio of their specific resistance would be
(a)1:2 (b)8:1 (c)1:8 (d) 1:1
For Questions 13 to 16, two statements are given –one labelled Assertion (A) and other
labelled Reason (R). Select the correct answer to these questions from the options as
given below.
A. If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
B. If both Assertion and Reason are true but Reason is not the correct explanation of
Assertion.
C. If Assertion is true but Reason is false.
D. If both Assertion and Reason are false.
2
Q.13 Assertion: A charge, whether stationary or in motion produces a magnetic field round it 1
Reason: Moving charges produce only electric field in the surrounding space.
Q.14 Assertion: Hydrogen atom consists of only one electron but its emission spectrum has many 1
lines.
Reason: Only Lyman series is found in the absorption spectrum of hydrogen atom whereas
in the emission spectrum, all the series are found.
Q.15 Assertion (A): Nuclei having mass number about 60 are least stable. 1
Reason (R): When two or more light nuclei are combined into a heavier nucleus then the
binding energy per nucleon will decrease
Q.16 Assertion (A): de Broglie's wavelength of a freely falling body keeps decreasing with time. 1
Reason (R): The momentum of the freely falling body increases with time.
[SECTION – B]
Q.17 Name the constituent radiation of electromagnetic spectrum which is: 2
a. used to study crystal structure
b. suitable for radar systems used in aircraft navigation.
Write one another application of each of these radiations.
Q.18 Two similar bars, made from two different materials P and Q, are placed one by one, in a 2
non-uniform magnetic field. It is observed that
a) bar P tends to move from the weak to the strong field region.
b) bar Q tends to move from the strong to the weak field region.
Identify the magnetic material used for making these two bars. Show with the help of
diagrams, the behaviour of the field lines, due to an external magnetic field, near each of
these two bars.
Q.19 The Bohr radius of Hydrogen atom is 5.3 x 10-11 m. Find its radius in the first excited state. 2
Also calculate the total energy in this state.
Q.20 If an equiconvex lens of focal length f and power P is cut into half in thickness, 2
What is the focal length and power of each half?
Q.21 Define the terms depletion layer and Potential barrier. 2
OR
Draw the circuit diagram used to determine the VI characteristics of forward and reverse
biasing.
[SECTION -C]
Q.22 Determine the angular separation between central maximum and first order maximum of 3
the diffraction pattern due to a single slit of width 0.25mm when light of wavelength
5890A0 is incident on it normally.
Q.23 An inductor L of reactance XL is connected in series with a bulb B and an AC source. How 3
would the brightness of the bulb change when?
a) The number of turns in the inductor is reduced
b) An iron rod is inserted in the inductor and
c)A capacitor of reactance XC = XL is inserted in series in the circuit. Justify your answer in
each case.
Q.24 A hollow cylindrical box of length 1m and area of cross-section 25 cm2 is placed in a three 3
dimensional coordinate system as shown in the figure. The electric field in the region is
given by vector E = 50x where E is in NC-1 and x is in metres. Find
a.Net flux through the cylinder.
3
b. Charge enclosed by the cylinder.
Q.25 State Gauss’s theorem in electrostatics. Using this theorem, derive an expression for the 3
electric field due to an infinitely long straight wire of linear charge density λ.
OR
Use Gauss’s law to obtain the expression for the electric field due to a uniformly charged
infinite plane sheet of charge.
Q.26 (I) Draw a ray diagram for the formation of image by a Cassegrain telescope. 3
(II)Why these types of telescopes are preferred over refracting type telescopes
Q.27 Write Einstein’s photoelectric equation and mention which important features in 3
photoelectric effect can be explained with the help of this equation. The maximum kinetic
energy of the photo electrons gets doubled when the wavelength of light incident on the
surface changes 𝜆 1 from to 𝜆 2 . Derive the expressions for the threshold wavelength 𝜆 0
and work function for the metal surface.
Q.28 Sketch the curve for binding energy per nucleon vs mass number. write the significance 3
of it.
[SECTION E]
Case Study Based Question:Q.NO.29-30 4
Q29 FORCE ON A MOVING CHARGE
Stationary charge creates an electric field but a moving charge creates a Magnetic field also
that can affect other moving charges. It was observed by Oersted. He saw that if a magnetic
needle is placed near current carrying wire it shows slight deflection. The direction of the
magnetic field can be determined by using the Right hand thumb rule. Magnetic field is the
space around a magnet, a current carrying conductor up to which it can attract or repel
magnetic material. Force on a moving charge in magnetic field is given by the formula =
q( X )
Where q = charge on particle
v = velocity of charge particle
B = magnetic field and
F = magnetic force
When a current carrying conductor is placed in an external magnetic field, it experiences a
mechanical force. A conductor of length l carrying current i
held in a magnetic field B at an angle θ with it, experiences a force given by
F = IlB sin θ.
i. Moving charge can create
(A) Electric field (B) magnetic field
(C) Both electric and magnetic field (D) none of them
ii. If a current is flowing from south to north in a straight wire what will be the
direction of magnetic field to its left side
(A) Outward (B) inward (C) Towards right (D) towards left
iii. Which of the following cannot be the source of magnetic field?
(A) Current carrying wire (B) moving electron
(C) Moving proton (D) stationary charge
4
iv. Force acting on a conductor of length 10 m carrying a current of 6A kept
perpendicular to the magnetic field of 2T is
(A) 60N (B) 120N (C) 90N (D) 100N
OR
Any charge particle q enter along the magnetic field B then force experience by charge
particle is
(A) Maximum (B) minimum (C) zero (D) qvB
Q.30 p-n junction is a semiconductor diode. It is obtained by bringing p-type semiconductor in 4
close contact with n- type semiconductor. A thin layer is developed at the p- n junction
which is devoid of any charge carrier but has immobile ions. It is called depletion layer. At
the junction a potential barrier appears, which does not allow the movement of majority
charge carriers across the junction in the absence of any biasing of the junction. p-n junction
offers low resistance when forward biased and high resistance when reverse biased.
i. In the middle of depletion layer of reverse biased p- n junction, the
(A). Electric field is zero (B). Potential is zero
(C.) Potential is maximum (D). Electric field is maximum
ii. The energy band gap is maximum in
(A). Metals (B). Superconductors
(C). Insulators (D). Semiconductors
iii. The number of majority carriers crossing the junction of diode depends primarily on the
(A) Concentration of doping impurities (B)Magnitude of potential barriers
(C) Magnitude of the forward bias voltage
(D) Rate of thermal generation of electron –hole pairs
iv. Hole is -
(A) Antiparticle of electron (B) A vacancy created when an electron leaves
covalent bond
(C) Absence of free electrons (D)An artificially created particle.
[SECTION E]
Q.31 Define wave-front. (i) draw the shape of refracted wave-front when the plane incident 5
wave undergoes refraction from optically denser medium to rarer medium. Hence prove
Snell’s law of refraction (ii) When light travels from a rarer to a denser medium, the speed
decreases. Does the reduction in speed imply a reduction in the energy carried by the light
wave?
OR
(a) Trace the rays of light showing the formation of an image due to a point object placed
on the axis of a spherical surface separating the two media of refractive indices n1 and n2
Establish the relation between the distances of the object, the image and the radius of
curvature from the central point of the spherical surface
(b). A converging lens of refractive index 1.5 is kept in a liquid medium having same
refractive index. What would be the focal length of the lens in this medium?
Q.32 (a) Derive the condition for balance in a Wheatstone bridge with help of Kirchhoff law. 5
(b) Find potential difference between A and B in the given circuit shown.
5
OR
(a) What is internal resistance of a cell. Write two factors on which it depends.
(b) Two cells of e.m.fs and internal resistances E1,r1 and E2,r2 are connected in parallel.
Obtain expressions for the equivalent emf and resistance of the combination.
Q.33 (i) Explain briefly, with the help of a labelled diagram, the basic principle of the working of 5
an a.c. generator.
(ii) In an a.c. generator, coil of N turns and area A is rotated at an angular velocity ω in a
uniform magnetic field B. Derive an expression for the instantaneous value of the emf
induced in coil.
(iii) What is the source of energy generation in this device?
OR
(a) With the help of a diagram, explain the principle of a device which changes a low ac
voltage into a high voltage.
(b) Deduce the expression for the ratio of secondary voltage to the primary voltage in terms
of the ratio of the number of turns of primary and secondary winding. For an ideal
transformer, obtain the ratio of primary and secondary currents in terms of the ratio of the
voltages in the secondary and primary coils.
(c) Write any two sources of the energy losses which occur in actual transformers.
