CLASS–XII
PHYSICS (2025–26)
Time: 3 Hours
Theory: 70 Marks
General Instructions
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The question paper consists of 18 questions.
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Question No 1 carries 20 objective type questions of 1 mark each (15 Multiple Choice Questions and 5 True/False statements), covering knowledge and understanding.
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Questions number 2 to 8 (7 questions) are short answer type, carrying 2 marks each. Internal choice is provided in Questions 6, 7, and 8.
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Questions number 9 to 15 (7 questions) are short/medium answer type, carrying 3 marks each. Internal choice is provided in Questions 13, 14, and 15.
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Question 16 is a comprehension type question carrying 5 marks (5 sub-questions of 1 mark each).
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Questions 17 and 18 are long answer type, carrying 5 marks each, with internal choice for each question. Question 18 has a choice between one Ray Optics question and one Wave Optics question.
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Un-programmable calculators and log tables are allowed.
Section A (Objective Type Questions)
Q.1. Choose the correct option (15 Marks)
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The capacitance of a parallel plate capacitor increases when air is replaced by a medium of dielectric constant K because:
(a) The electric field strength increases.
(b) The effective area of the plates increases.
(c) The potential difference across the plates decreases.
(d) The charge density increases. -
What happens to the drift velocity of free electrons in a metallic conductor when the temperature is increased?
(a) Increases
(b) Decreases
(c) Remains constant
(d) Increases exponentially -
The force acting on a current-carrying conductor placed in a uniform magnetic field is zero if the angle between the conductor and the magnetic field is:
(a) 90°
(b) 45°
(c) 0° or 180°
(d) 60° -
The Lorentz force is the sum of:
(a) Gravitational force and Electrostatic force
(b) Magnetic force and Gravitational force
(c) Electrostatic force and Magnetic force
(d) Nuclear force and Magnetic force -
A transformer works on the principle of:
(a) Self-induction
(b) Eddy currents
(c) Mutual induction
(d) Joule heating -
Which part of the electromagnetic spectrum carries the minimum frequency?
(a) X-rays
(b) Visible light
(c) Gamma rays
(d) Radio waves -
The relation between critical angle (C) and the refractive index (μ) of a medium is:
(a) C = 1/μ
(b) μ = sin C
(c) μ = 1/sin C
(d) C = tan⁻¹(μ) -
The shape of the interference fringes obtained in Young's Double Slit Experiment on a screen placed perpendicular to the path of light is:
(a) Parabola
(b) Hyperbola
(c) Ellipse
(d) Circle -
If a photosensitive metal is illuminated by light of frequency ν (ν > ν₀), the maximum kinetic energy of the emitted photoelectrons is given by:
(a) h(ν - ν₀)²
(b) h(ν - ν₀)
(c) hν
(d) hν + φ₀ -
The existence of the nucleus in an atom was first established by:
(a) Bohr's model
(b) Thomson's model
(c) α-particle scattering experiment
(d) Positive ray analysis -
The binding energy per nucleon is maximum for which nucleus?
(a) ⁴He
(b) ¹⁶O
(c) ⁵⁶Fe
(d) ²³⁸U -
The correct order of forbidden energy gaps (E₁, E₂, E₃) for conductor, semiconductor, and insulator, respectively, is:
(a) E₁ > E₂ > E₃
(b) E₁ < E₂ < E₃
(c) E₁ = E₂ < E₃
(d) E₁ ≈ 0, E₂ < E₃ -
The SI unit of electric dipole moment is:
(a) C/m
(b) C m
(c) C m²
(d) N m -
The power factor in an LCR series circuit at resonance is:
(a) Zero
(b) Unity (1)
(c) Between 0 and 1
(d) Infinite -
Consider three charged bodies P, Q, R. If P and Q repel each other, and P attracts R. What is the nature of the force between Q and R?
(a) Attractive
(b) Repulsive
(c) Net force zero
(d) Cannot be determined
Q.1. State True or False (5 Marks)
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The magnetic susceptibility of a paramagnetic substance has a negative value.
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The average power consumed by an AC circuit over half a cycle is zero.
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If the refractive index of water is 4/3 and that of glass is 3/2, the refractive index of water w.r.t. glass is 9/8.
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Electron emission can only be obtained through the photoelectric effect.
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When a nucleus emits one α particle and one β⁻¹ particle, the mass number decreases by 4 and the atomic number decreases by 2.
Section B (Short Answer Questions) (2 Marks Each)
Q.2 Name two electromagnetic radiations that are used in medicine. Give one use of each.
Q.3 Define a hole in a semiconductor. What is the effective charge associated with a hole?
Q.4 State the composition (particles present) and typical size (order of magnitude) of an atomic nucleus.
Q.5 What is the main function of the soft iron core used inside a moving coil galvanometer?
Q.6 (A) Define continuous charge distribution and state the superposition principle for electric forces.
OR
(B) Three capacitors of capacitance 3 μF, 6 μF, and 2 μF are connected in series across a 10 V battery. Calculate the equivalent capacitance of the combination.
Q.7 (A) Why are the coils of a resistance box generally made of doubled or bifilar wire?
OR
(B) A carbon resistor has color bands Brown, Green, Yellow, and Silver. Write down the value of the resistance including tolerance.
Q.8 (A) Define the terms threshold frequency (ν₀) and work function (φ₀) in the context of photoelectric emission.
OR
(B) The work function of a metal is 3.0 eV. If light of frequency 8.0 × 10¹⁴ Hz is incident on it, calculate the maximum kinetic energy of the emitted photoelectrons in eV. (Use h = 4.14 × 10⁻¹⁵ eV·s).
Section C (Medium Answer Questions) (3 Marks Each)
Q.9 Define electric potential energy. Derive the relation for the electric potential energy of a system consisting of two point charges q₁ and q₂ separated by a distance r.
Q.10 Discuss the variation of resistivity with temperature in the case of (i) Metals, (ii) Semiconductors, and (iii) Insulators.
Q.11 State the principle of Rutherford's alpha-particle scattering experiment. Explain the concept of the distance of closest approach based on this experiment.
Q.12 Draw the circuit diagram for a p-n junction diode and show its I-V characteristics (graph) under both forward bias and reverse bias conditions. Briefly explain the shape of the curve in both cases.
Q.13 (A) Write the expression for the magnetic field intensity (B) due to a magnetic dipole (Bar Magnet) along its axial line. Define the magnetic dipole moment.
OR
(B) A galvanometer coil has a resistance of 100 Ω and gives full-scale deflection for a current of 10 mA. Calculate the value of the shunt resistance required to convert it into an ammeter of range 0 to 1 A.
Q.14 (A) State Lenz's Law for electromagnetic induction. Explain how this law demonstrates the conservation of energy.
OR
(B) The magnetic flux φ linked with a coil varies with time t as φ = 6 t² – 2t + 5. Find the magnitude of the induced e.m.f. in the coil at t = 1 s.
Q.15 (A) Derive the expression for the prism formula (μ = sin((A+δm)/2)/sin(A/2)) assuming the angle of the prism (A) is very small.
OR
(B) A convex lens (focal length f₁ = 40 cm) and a concave lens (f₂ = -20 cm) are placed coaxially in contact. Calculate the power and the nature of the combination. If an object is placed 80 cm away from the combination, where is the final image formed?
Section D (Long Answer and Comprehension Questions) (5 Marks Each)
Q.16 (Comprehension Type Question)
Read the following paragraph and answer the questions below:
Biot-Savart Law is a fundamental principle in magnetostatics, detailing how an electric current creates a magnetic field. It relates the differential magnetic field (dB) produced by a current element (I dl) to the distance (r) from the element and the direction. When analyzing current distributions, such as the field along the axis of a circular current-carrying loop or the force experienced by two parallel current-carrying wires, Biot-Savart Law proves essential. The concept of magnetism also extends to materials, which are categorized based on their response to an external magnetic field, such as dia-, para-, and ferro-magnetic substances. For instance, diamagnetic substances are weakly repelled by external magnetic fields.
Questions (1 × 5 = 5 Marks):
(1) State the mathematical proportionality of dB to the distance r according to the Biot-Savart Law.
(2) What is the expression for the magnetic field along the axis of a current-carrying circular loop (no derivation required)?
(3) How does the Lorentz force determine the direction of the force exerted on a positive charge moving in a magnetic field?
(4) Define the S.I. unit of current, Ampere, based on the force between two parallel current-carrying conductors.
(5) Give one example of a diamagnetic substance.
Q.17
(A) State Gauss’s Theorem in electrostatics. Use it to find the expression for the electric field intensity (E) due to a uniformly charged thin spherical shell (hollow conductor) at a point (i) outside the shell, (ii) on the surface of the shell, and (iii) inside the shell.
OR
(B) Define electric dipole moment. Find the relation for electric potential at an arbitrary point due to an electric dipole. Write down the special case relations for potential on the axial line and the equatorial plane.
Q.18
(A) Draw a labeled ray diagram of an Astronomical Refracting Telescope when the final image is formed at infinity (Normal Adjustment). Derive the expression for its magnifying power in this configuration.
OR
(B) State the necessary conditions for a sustained interference pattern of light to be observed. Derive an expression for the fringe width (β) in Young's double slit experiment.
