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ISC Class XII Board Exam 2026 : Physics

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Taneesha Som
Auxilium Convent School, Dum Dum, Kolkata
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The Physics Axiom where every Why finds its How Santanu Saha | B.Sc. (Physics), B.Tech. & M.Tech. (RPE) | 14+ years of experience Phone: 8777053221 HALF YEARLY EXAMINATION CLASS XII PHYSICS (THEORY) Maximum Marks: 70 Time Allowed: 3 Hours General Instructions: Candidates are allowed additional 15 minutes for only reading the paper. They must NOT start writing during this time. All questions are compulsory. This question paper is divided into 4 Sections A, B, C and D. Section A comprises of 14 marks (7 MCQs and 7 Assertion-Reasoning). Section B comprises of 7 questions of 2 marks each. Section C comprises of 9 questions of 3 marks each. Section D comprises of 3 questions of 5 marks each. Use of physical constants: c = 3 108 m/s, h = 6.63 10 34 Js, e = 1.6 10 19 C, 0 = 8.85 10 12 F/m, 0 = 4 10 7 T m/A, 1 u = 931.5 MeV. SECTION A (14 Marks) Question 1: Choose the correct option for the following questions. [7 1 = 7] (i) An electric charge q is placed at the centre of a cube. The electric flux passing through one of its faces is: (a) q/ 0 (b) q/6 0 (c) q/4 0 (d) Zero (ii) The drift velocity of electrons in a copper wire of length L under a potential difference V is vd . If the length is doubled keeping V constant, the new drift velocity will be: (a) vd /2 (b) vd (c) 2vd (d) vd /4 (iii) A moving coil galvanometer can be converted into a voltmeter by connecting a: (a) high resistance in series (b) low resistance in parallel (c) high resistance in parallel (d) low resistance in series (iv) According to Lenz s law, the induced emf opposes the change that produces it. This is a direct consequence of the law of conservation of: (a) charge (b) momentum (c) energy (d) mass (v) In Young s double slit experiment, if the distance between the slits is halved and the distance between the slits and the screen is doubled, the fringe width becomes: (a) unchanged (b) half (c) double (d) four times (vi) The minimum energy required to remove an electron from the surface of a metal is called: (a) Kinetic energy (b) Stopping potential (c) Work function (d) Activation energy (vii) In a p-type semiconductor, the majority and minority charge carriers are respectively: (a) electrons and holes (b) holes and electrons (c) protons and electrons (d) electrons and protons Question 2: Assertion-Reasoning Type Questions [7 1 = 7] Direction: In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R). Choose the correct option: (a) Both A and R are true and R is the correct explanation of A. The Physics Axiom where every Why finds its How Santanu Saha | B.Sc. (Physics), B.Tech. & M.Tech. (RPE) | 14+ years of experience Phone: 8777053221 (b) Both A and R are true but R is NOT the correct explanation of A. (c) A is true but R is false. (d) A is false but R is true. (i) Assertion: The electric field inside a hollow conducting sphere is zero. Reason: Charges given to a conductor always reside on its outer surface. (ii) Assertion: Kirchhoff s junction rule is based on the conservation of charge. Reason: The algebraic sum of currents meeting at a junction in a closed circuit is zero. (iii) Assertion: A charged particle moving parallel to a magnetic field experiences zero magnetic force. Reason: The magnetic force acting on a charge is given by F = qvB sin , and here = 0 . (iv) Assertion: The self-inductance of a coil is often referred to as electrical inertia. Reason: It opposes any change in the current flowing through the circuit. (v) Assertion: Diffraction limits the resolving power of optical instruments. Reason: The wave nature of light causes the spreading of light around small obstacles. (vi) Assertion: The de Broglie wavelength of an electron accelerated through V volts is proportional to 1/ V . Reason: The kinetic energy of the electron gained is equal to eV . (vii) Assertion: The energy gap in semiconductors is very large (greater than 3 eV). Reason: In semiconductors, electrons are tightly bound to the nucleus at room temperature. SECTION B (14 Marks) Question 3. Three capacitors of 2 F, 3 F, and 6 F are joined in series and the combination is connected to a 10 V battery. Calculate the equivalent capacitance and the charge on each capacitor. [2] Question 4. Draw a labelled circuit diagram to study the V-I characteristics of a p-n junction diode in forward bias. Also, draw the characteristic curve. [2] Question 5. A long straight wire carries a steady current of 35 A. What is the magnitude of the at a point 20 cm from the wire? magnetic field B [2] Question 6. The current in a coil drops from 5.0 A to 0.0 A in 0.1 s. If the average emf induced in the coil is 200 V, calculate the self-inductance of the coil. [2] Question 7. Calculate the de Broglie wavelength associated with an electron accelerated from rest through a potential difference of 100 V. [2] Question 8. Draw a neat labelled energy level diagram for the hydrogen atom, clearly showing the spectral transitions corresponding to the Lyman and Balmer series. [2] Question 9. Define internal resistance of a cell. State any two factors on which it depends. [2] SECTION C (27 Marks) Question 10. Three point charges +10 C, +5 C, and 5 C are placed at the vertices A, B, and C respectively of an equilateral triangle of side 10 cm. Calculate the total electrostatic potential energy of the system. [3] The Physics Axiom where every Why finds its How Santanu Saha | B.Sc. (Physics), B.Tech. & M.Tech. (RPE) | 14+ years of experience Phone: 8777053221 Question 11. A cell of emf E and internal resistance r is connected across a variable external resistance R. (a) Plot a graph showing the variation of terminal voltage V with the external resistance R. (b) If a current of 2 A flows when R = 4 , and 1.5 A flows when R = 6 , calculate the emf E and internal resistance r of the cell. [1+2=3] Question 12. Using Biot-Savart s law, derive an expression for the magnetic field at the centre of a circular current-carrying coil of radius r having N turns. [3] Question 13. The magnetic flux linked with a closed coil is given by the equation = 5t2 +3t+16 (in Webers), where t is the time in seconds. Find the magnitude of the induced emf in the coil at t = 4 s. State the law used to find the direction of this induced emf. [3] Question 14. In Young s double slit experiment, the two slits are separated by a distance of 0.28 mm and the screen is placed 1.4 m away from the slits. The distance between the central bright fringe and the fourth bright fringe is measured to be 1.2 cm. Determine the wavelength of light used in the experiment. [3] Question 15. State Huygens principle. Using this principle, draw a neat diagram to show the refraction of a plane wavefront incident on the boundary separating a rarer medium from a denser medium. [3] Question 16. The work function of a certain metal is 2.14 eV. When monochromatic light of frequency 6 1014 Hz is incident on the metal surface, photoemission of electrons occurs. Find: (a) the energy of the incident photons (in eV). (b) the maximum kinetic energy of the emitted electrons. (c) the stopping potential. [3] Question 17. Calculate the mass defect and the binding energy per nucleon for the 8 O16 nucleus. Given: Mass of 8 O16 nucleus = 15.99491 u, Mass of proton mp = 1.00783 u, Mass of neutron mn = 1.00867 u. [3] Question 18. Based on the energy band theory of solids, distinguish between metals, insulators, and semiconductors by drawing their respective energy band diagrams. [3] SECTION D (15 Marks) Question 19. (a) State Gauss s theorem in electrostatics. [1] (b) Using this theorem, derive an expression for the electric field intensity due to a uniformly charged infinite plane sheet. [2] (c) An infinite line charge produces an electric field of 9 104 N/C at a perpendicular distance of 2 cm. Calculate the linear charge density of the wire. [2] Question 20. (a) State Kirchhoff s two laws of electrical networks. [2] (b) Draw the circuit diagram of a Wheatstone bridge and write the mathematical condition for its balance. [1] (c) Four resistors P = 10 , Q = 20 , R = 30 , and S = 60 form a Wheatstone bridge. A cell of emf 5 V and negligible internal resistance is connected across the bridge. Calculate the total current drawn from the cell when the bridge is balanced. [2] Question 21. (a) State Bohr s three postulates for the hydrogen atom model. [1.5] (b) Using these postulates, derive the mathematical expression for the radius of the nth stationary orbit of the hydrogen atom. [2] The Physics Axiom where every Why finds its How Santanu Saha | B.Sc. (Physics), B.Tech. & M.Tech. (RPE) | 14+ years of experience Phone: 8777053221 (c) Calculate the total energy (in eV) of an electron present in the second excited state (n = 3) of the hydrogen atom. [1.5]

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