ISC Class XII Board Examination

ISC Physics (Paper 1 — Theory) — Board Examination 2025

Board2025Subject code 861

Board: ISC Class XII Board Examination
Class: Class 12
Subject: Physics
Year: 2025
Total marks: Not verified
Duration: Not verified

Verification and rights

Follows the published ICSE syllabus structure and links back to the source, but has not been reconciled line by line against a Council document.

Imported board paper from Oswaal Books (reproduction of CISCE board paper) on 2026-08-29.

Questions in this paper

1((i))But it is observed that they are attracting each other. (A) In questions (i) to (vii) given below, choose the What change should the student make for the wires correct alternative (a), (b), (c) or (d). to repel each other? [1]
When a battery is connected between the terminals R1 R2
P and Q, as shown in Figure 1 below, it is found MS
that no current flows through 5Ω resistor. Then, the
value of resistor X is:
P
10 10 E1 E2
25 X NT
Q Figure 2
Figure 1 (a) Reverse the terminals of batteries E1 and E2.
(a) 10 Ω (b) 20 Ω (b) Reverse the terminals of battery E1 or E2.
(c) 25 Ω (d) 45 Ω (c) Choose supply voltage such that E1 = E2.1 mark
1((ii))But it is observed that they are attracting each other. (A) In questions (i) to (vii) given below, choose the What change should the student make for the wires correct alternative (a), (b), (c) or (d). to repel each other? [1]
The relative permeability of substance ‘X’ is slightly (d) Add key and ammeter to the circuit.
less than one and that of substance ‘Y’ is slightly (v) N-type semiconductor is that which has:
more than one. Then: (a) majority of holes as charge carriers.
(a) ‘X’ is paramagnetic and ‘Y’ is ferromagnetic. (b) majority of free electrons as charge carriers.
(b) ‘X’ is diamagnetic and ‘Y’ is ferromagnetic. (c) trivalent element added as an impurity.
(c) ‘X’ is paramagnetic and ‘Y’ is diamagnetic. (d) an equal number of holes and free electrons.
(d) ‘X’ is diamagnetic and ‘Y’ is paramagnetic. (vi) Given below are two statements marked, Assertion1 mark
1((iii))But it is observed that they are attracting each other. (A) In questions (i) to (vii) given below, choose the What change should the student make for the wires correct alternative (a), (b), (c) or (d). to repel each other? [1]
If kinetic energy of moving electrons is made four and Reason. Read the two statements and choose
times, then their de Broglie wavelength becomes: the correct option.
Assertion: When a convex lens made of glass is1 mark
1((vii))But it is observed that they are attracting each other. (A) In questions (i) to (vii) given below, choose the What change should the student make for the wires correct alternative (a), (b), (c) or (d). to repel each other? [1]
Given below are two statements marked, Assertion
and Reason. Read the two statements and choose E
the correct option. Figure 4 Figure 5
Assertion: Diffraction of light is difficult to observe
in everyday situations but can be observed in (a) In which of the two combinations, emf of the
laboratory conditions. battery is greater?
Reason: To produce diffraction of waves, size of an (b) When a resistor ‘R’ is connected between the
obstacle must be comparable to the wavelength of terminals P and Q, I1 and I2 are the currents
the waves. flowing through ‘R’ in Figure 4 and Figure 5
(a) Both Assertion and Reason are true and Reason I
respectively. Obtain the ratio 1 .
is the correct explanation for Assertion. I2
(b) Both Assertion and Reason are true but Reason
3((i))2] is not the correct explanation for Assertion. In case of a short electric dipole: (c) Assertion is true and Reason is false.
What is the locus of a point having zero potential?
(d) Both Assertion and Reason are false.
3((ii))2] is not the correct explanation for Assertion. In case of a short electric dipole: (c) Assertion is true and Reason is false.
If electric field intensity at a point in axial position is
(B) Answer the following questions briefly: E1 and at an equidistant point in equatorial position
3((i) [cont.])2] is not the correct explanation for Assertion. In case of a short electric dipole: (c) Assertion is true and Reason is false.
How does the resistance of a semiconductor crystal E
vary with its temperature? is E2, what is the ratio 1 ?
E2
3((ii) [cont.])2] is not the correct explanation for Assertion. In case of a short electric dipole: (c) Assertion is true and Reason is false.
Figure 3 below shows an ideal transformer. Explain
4((iii))2] why current flowing through secondary coil is greater than that in primary coil. [1] (i) Figure 6 below shows an electric circuit. 3A 4 Q 1 4A P R Core Primary coil Secondary coil 10 V (input) (output) E S Figure 6 Apply Kirchhoff’s laws to calculate: Figure 3 (a) current ‘I’ flowing through the 2 Ω resistor.
State any one difference between a primary rainbow (b) emf of the cell ‘E’.
and a secondary rainbow. OR
4((iv))2] why current flowing through secondary coil is greater than that in primary coil. [1] (i) Figure 6 below shows an electric circuit. 3A 4 Q 1 4A P R Core Primary coil Secondary coil 10 V (input) (output) E S Figure 6 Apply Kirchhoff’s laws to calculate: Figure 3 (a) current ‘I’ flowing through the 2 Ω resistor.
Hubble telescope employs a large parabolic mirror
4((ii))2] why current flowing through secondary coil is greater than that in primary coil. [1] (i) Figure 6 below shows an electric circuit. 3A 4 Q 1 4A P R Core Primary coil Secondary coil 10 V (input) (output) E S Figure 6 Apply Kirchhoff’s laws to calculate: Figure 3 (a) current ‘I’ flowing through the 2 Ω resistor.
In a potentiometer experiment, a cell of emf 1.25 V
as an objective. State any one advantage of using a
gives a balance point at 35 cm mark of the wire. If
mirror in place of a lens in such a telescope.
this cell is replaced by another cell, the balance point1 mark
4((v))2] why current flowing through secondary coil is greater than that in primary coil. [1] (i) Figure 6 below shows an electric circuit. 3A 4 Q 1 4A P R Core Primary coil Secondary coil 10 V (input) (output) E S Figure 6 Apply Kirchhoff’s laws to calculate: Figure 3 (a) current ‘I’ flowing through the 2 Ω resistor.
Name any one phenomenon where moving particles
is at 63 cm mark. Calculate the emf of the second cell.
behave like waves.1 mark
4((vi))2] why current flowing through secondary coil is greater than that in primary coil. [1] (i) Figure 6 below shows an electric circuit. 3A 4 Q 1 4A P R Core Primary coil Secondary coil 10 V (input) (output) E S Figure 6 Apply Kirchhoff’s laws to calculate: Figure 3 (a) current ‘I’ flowing through the 2 Ω resistor.
What is the minimum energy a gamma ray (γ) Question 5
photon should possess to produce an electron – Magnetic field at the centre of a circular coil is B.
positron pair? Calculate the magnetic field at the same point when2 marks
4((vii))2] why current flowing through secondary coil is greater than that in primary coil. [1] (i) Figure 6 below shows an electric circuit. 3A 4 Q 1 4A P R Core Primary coil Secondary coil 10 V (input) (output) E S Figure 6 Apply Kirchhoff’s laws to calculate: Figure 3 (a) current ‘I’ flowing through the 2 Ω resistor.
In an energy band diagram of a certain material, each of the current, number of turns of the coil and
forbidden band is absent. Identify this material. its radius is doubled.
SECTION-B (14 MARKS) Question 62 marks
2((i))2] The objective of a telescope consists of two lenses kept in contact. One lens has an optical power of
(a) What is the effect on capacitance of a parallel
+2.0 D whereas the other lens has an optical power
plate capacitor if the distance between its plates is
of-1.5 D. Calculate focal length of the objective.
increased?
7((i))2] Satellite v(V) 2.5 2.0 1.5 1.0 0.5 Dish Antenna 0.1 0.2 0.3 0.4 0.5 i(A) (1) emf (E) of the cell.
Name the electromagnetic wave travelling from the
satellite to the dish antenna shown in the image (2) Internal resistance (r) of the cell.
above. OR
7((ii))2] Satellite v(V) 2.5 2.0 1.5 1.0 0.5 Dish Antenna 0.1 0.2 0.3 0.4 0.5 i(A) (1) emf (E) of the cell.
If the wavelength of an electromagnetic wave is (ii) The graph below shows the variation of current
6 nm, what is its frequency? density (J) with electric field (E) applied to two
8((ii))2] different metallic wires A and B. J B With reference to photoelectric effect, define the terms:
Work function.
SECTION-C (27 MARKS)
E
9((i))3] (a) Which one of the wires, A or B, has higher An infinite plane metallic sheet having surface resistivity? charge density ‘+σ’ is placed in vacuum. P is a point (b) For a certain value of electric field (E), in which at a small distance ‘r’ to its right. wire ‘A’ or ‘B’ is drift velocity greater? Give a
Write an expression for intensity of electric field at
point P. reason for your answer.
9((ii))3] (a) Which one of the wires, A or B, has higher An infinite plane metallic sheet having surface resistivity? charge density ‘+σ’ is placed in vacuum. P is a point (b) For a certain value of electric field (E), in which at a small distance ‘r’ to its right. wire ‘A’ or ‘B’ is drift velocity greater? Give a
Now, an identical charged sheet having surface Question 11
charge density ‘-σ’ is placed parallel to the first A galvanometer having a resistance of 20 Ω shows
sheet such that the point P is to its left at the same a full scale deflection with a current of 1 mA. How
distance ‘r’. (The point P lies between the two plates.) can it be converted into a voltmeter with a range of
(a) What is the resultant intensity of electric field at 0–10 V?
point P? Question 12
(b) What is its direction? (i) Two infinitely long straight wires PQ and RS
carrying currents I1 and I2 respectively are kept3 marks
10((i))3] 10 cm apart in vacuum. Calculate magnetic field (B)
Harry sets up a circuit as shown in Figure 7 below. at the point X shown in Figure 8 below.
He measures potential difference ‘V’ across the P R
variable resistor R with an instrument Y. He also
measures current ‘I’ flowing through R with another I1 = 4A I2 = 16A
instrument X. 2 cm
Y X
10 cm
Q S
R
I Figure 8
X OR
10((ii))3] 10 cm apart in vacuum. Calculate magnetic field (B)
An electron and a proton are moving along the +X
axis. If an external magnetic field B = 0.314 T is
E, r applied along -Z axis:
Figure 7 (a) What is the path followed by the electron due to
(a) Identify the instruments X and Y.
the magnetic field?
(b) Using the graph of V against I shown below,
(b) Calculate the frequency of revolution of the
calculate proton.
13((i))2] If the position of the rod changes with time as x = πt, A convex lens having small focal length is to be used where x is in metre and t is in second, then: as a magnifying glass (simple microscope) to obtain (1) Calculate the motional emf developed in the an image of a small diamond. If the image lies at rod. least distance of distinct vision (D): (2) Name the law used to find the direction of
Where will you keep the diamond to obtain its induced current.
image at D? (b) When current flowing through a solenoid decreases
13((ii))2] If the position of the rod changes with time as x = πt, A convex lens having small focal length is to be used where x is in metre and t is in second, then: as a magnifying glass (simple microscope) to obtain (1) Calculate the motional emf developed in the an image of a small diamond. If the image lies at rod. least distance of distinct vision (D): (2) Name the law used to find the direction of
State any two characteristics of the image formed by from 15 A to 0 in 0.2 s, an emf of 30 V is induced in
the magnifying glass. it. Calculate the coefficient of self-inductance of the
14((i))3] solenoid. A parallel beam of light is travelling obliquely from OR an optically rarer medium to an optically denser (ii) An alternating emf E = 5.0 sin(314 t)V is applied to a medium. circuit containing a resistor connected in series with
Draw a labelled diagram showing incident and an unknown component X.
refracted wavefronts. Mark angle of incidence as ‘i’ The current in the circuit is found to be I = 3.0 sin
and angle of refraction as ‘r’.  π
14((ii))3] solenoid. A parallel beam of light is travelling obliquely from OR an optically rarer medium to an optically denser (ii) An alternating emf E = 5.0 sin(314 t)V is applied to a medium. circuit containing a resistor connected in series with
Use Huygen’s wave theory to prove Snell’s law.  314t - 3  A.
 
16((i))3] (i) (a) Show that radius (rn) of the n Bohr orbit varies Two identical rectangular slits 5 mm apart are directly with square of the principal quantum illuminated with a monochromatic light of number (n) of the orbit. wavelength 600 nm. The screen is kept 1.2 m away (b) (1) Where does nuclear fusion reaction take place from the slits. continuously in the Universe?
Calculate the distance between the 5th bright fringe (2) What is meant by “Mass defect” of a nucleus?
(band) on one side and the 3rd bright fringe on the
OR
other side of the central bright band.
16((ii))3] (i) (a) Show that radius (rn) of the n Bohr orbit varies Two identical rectangular slits 5 mm apart are directly with square of the principal quantum illuminated with a monochromatic light of number (n) of the orbit. wavelength 600 nm. The screen is kept 1.2 m away (b) (1) Where does nuclear fusion reaction take place from the slits. continuously in the Universe?
(a) A group of students went on an educational tour
16((ii) [cont.])3] (i) (a) Show that radius (rn) of the n Bohr orbit varies Two identical rectangular slits 5 mm apart are directly with square of the principal quantum illuminated with a monochromatic light of number (n) of the orbit. wavelength 600 nm. The screen is kept 1.2 m away (b) (1) Where does nuclear fusion reaction take place from the slits. continuously in the Universe?
What will be the change in the interference pattern
to Bhabha Atomic Research Centre, Mumbai. They
if the given light is replaced with monochromatic
visited various nuclear reactors like Apsara, Cirus,
light of wavelength 500 nm?
Zerlina and Dhruv and observed that Apsara was a
17((i))3] swimming pool type reactor. The teacher explained
Plot a labelled graph of stopping potential (VS) how water slows down fast moving neutrons and
versus frequency (f) of incident UV radiation. absorbs the heat produced in the reactor.
17((ii))3] swimming pool type reactor. The teacher explained
State how the value of Planck’s constant can be
(1) What is the use of a nuclear reactor?
determined from this graph.
(2) What is the name given to a material which
SECTION-D (15 MARKS) slows down fast moving neutrons?
18((i))5] (3) State how a nuclear reactor can be shut down in
(a) Figure 9 shows a metallic rod AB of length case of an emergency.
l = 3 m moving in an (external uniform magnetic
(b) (1)
What is meant by the statement: ‘Angular
1 momentum of an orbiting electron is quantised’?
field, B =   T which is directed into the plane of
π (2) What is the physical significance of the fact that
this paper. total energy of an orbiting electron is negative?
B Question 20
When a television set (scientifically known as a
television receiver) is opened, many components
l V like semiconductor diodes, transistors, capacitors,
resistors, etc. can be observed on its motherboard.
There are different types of diodes like photo diode,
Zener diode, LED, etc. found in the T.V. set. With
A the help of these components, a television receives
Figure 9 audio as well as video signals.5 marks
18((i) [cont.])5] (3) State how a nuclear reactor can be shut down in
A semiconductor diode has two types of
USEFUL CONSTANTS AND RELATIONS
semiconducting materials: ‘P’ type and ‘N’ type.
1. Speed of light c = 3 × 108 ms-1
What is the difference between them? in vacuum
18((ii))5] (3) State how a nuclear reactor can be shut down in
Draw a labelled diagram of a full wave rectifier.
2. Charge of a e = 1.6 × 10-l9C
Show graphically how its output voltage varies proton
with time.
3. Mass of a mρ = 1.67 × 10-27 kg
18((iii))5] (3) State how a nuclear reactor can be shut down in
What type of diode can be used as a voltage
proton
regulator?
4. Permeability μ0 = 4π × 10-7 Hm-1
of vacuum
5. 1 nm = 10-9m
6. π = 3.14
