CBSE Class 12 Physics 2026 — Set 55/2/1

Which of the following materials has a positive and small value of magnetic susceptibility? (A) Cu (B) Al (C) Bi (D) Ni

A galvanometer of resistance 27Ω is converted into an ammeter of range (0-10)mA using a resistance of 3Ω. The galvanometer will show full scale deflection for a current of about (A) 10mA (B) 100mA (C) 1mA (D) 3mA

The magnetic flux φ (in Wb) linked with a coil is related to time t (in s) as φ = 5At² + Bt - 2C. The SI units of A and B are respectively (A) Wb s²,Wb s (B) Wb s⁻¹,Wb (C) Wb s⁻²,Wb s⁻¹ (D) Wb s⁻¹,Wb s⁻²

The figure shows the variation of capacitive reactance (XC) of two ideal capacitors of capacitances C₁ and C₂ with the reciprocal of angular frequency (1/ω) of an ac source. The value of C₁/C₂ is (A) (1)/(2) (B) 2 (C) √(3) (D) dfrac1√(3)

A magnet held vertically, with its north pole down, is dropped along the axis of a closed solenoid placed vertically on a table. If the observer looks down from the top, (A) the induced current will flow in the anticlockwise direction. (B) the induced current will flow in the clockwise direction. (C) no induced current will flow in the solenoid. (D) the magnet will fall with a constant velocity.

An electromagnetic wave is propagating along the x-axis. At any instant, the phase difference (in radian) between the electric field (vecE) and the magnetic field (vecB) associated with the wave is (A) zero (B) (π)/(4) (C) (π)/(2) (D) π

In Bohr model of hydrogen atom, the electron makes a transition from n = 5 to n = 1 state. As a result, a photon of wavelength λ is emitted. The wavelength of the photon emitted when an electron makes a transition from energy level n = 5 to n = 2 will be (A) (8)/(7)λ (B) (24)/(7)λ (C) (16)/(7)λ (D) (32)/(7)λ

Two statements are given – one labelled Assertion (A) and the other Reason (R). Select the correct answer from the codes below: (A) Both (A) and (R) are true and (R) is the correct explanation of (A). (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 and (R) is also false. Assertion (A) : On increasing the intensity of incident light of frequency nu(>nu₀) on a photosensitive surface, the photocurrent increases. Reason (R) : The stopping potential for a photosensitive surface increases with increase of frequency nu(>nu₀) of incident light.

Two statements are given – one labelled Assertion (A) and the other Reason (R). Select the correct answer from the codes below: (A) Both (A) and (R) are true and (R) is the correct explanation of (A). (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 and (R) is also false. Assertion (A) : On forward biasing a p-n junction diode, the height of the barrier potential increases. Reason (R) : In forward biasing of a p-n junction diode, the direction of the applied voltage is in the same direction as the built-in potential.

Two statements are given – one labelled Assertion (A) and the other Reason (R). Select the correct answer from the codes below: (A) Both (A) and (R) are true and (R) is the correct explanation of (A). (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 and (R) is also false. Assertion (A) : Light added to light can produce darkness. Reason (R) : When two coherent light waves interfere, there is darkness at the position of destructive interference.

Two statements are given – one labelled Assertion (A) and the other Reason (R). Select the correct answer from the codes below: (A) Both (A) and (R) are true and (R) is the correct explanation of (A). (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 and (R) is also false. Assertion (A) : Two electric heaters of power P₁ and P₂(>P₁) are joined in series across a dc source of voltage V. The power consumed by the combination will be less than that consumed by P₁ when connected across the same source. Reason (R) : The power consumed by an electric device when connected to a dc source of voltage V is proportional to its resistance.

Write two points of difference between intrinsic and extrinsic semiconductors.

Find the ratio ((λa)/(λp)) of the de Broglie wavelengths λa and λp associated respectively with an alpha particle and a proton, (i) if they are moving with the same kinetic energy; (ii) just after they are accelerated through the same potential difference.

A ray of light in air is incident at angle i on a face of an equilateral glass prism and is refracted through the prism. As i is varied, it is observed that the ray undergoes minimum deviation when i is three-fourth of the angle of the prism. Calculate the speed of light in the prism.

A heating element using nichrome is connected to a 220V supply. Initially it draws a current of 2.9A. After some time, the current attains a steady value of 2.5A. Find the steady temperature of the heating element if the room temperature is 27circC. The temperature coefficient of resistance of nichrome is 1.7×10⁻⁴circC⁻¹.

A 5cm long pencil is placed along the principal axis of a concave mirror of focal length 20cm such that its nearest end is at a distance of 25cm from the mirror. Calculate the length of the image of the pencil. OR In a Young's double-slit experiment, a beam of light consisting of two wavelengths 500nm and 600nm is used. The interference fringes are observed at a screen placed 1.8m away from the plane of the slits (slit separation 0.3mm). Calculate the least distance from the central maximum where the bright fringes due to both wavelengths coincide.

(a) Consider the following nuclides: ¹²₆C,¹⁹⁸₈₀Hg,¹⁴₆C,¹⁹⁷₇₉Au. Group them into isotopes and isotones. (b) How does the size of a nucleus depend on its mass number A? Hence prove that the density of a nucleus is a constant, independent of A, for all nuclei.

(a) An electric field vecE = E₀hati exists in a region of space. Draw three equipotential surfaces in the region. (b) Two point charges -q and +q are located at points (-a, 0, 0) and (a, 0, 0) respectively. Find the electrostatic potential at the point (x, 0, 0) where x gg a.

Name the electromagnetic waves which are used for (i) detection of fractures in bones, (ii) physiotherapy, (iii) radar systems. Also write their wavelength range.

(i) Define mutual inductance of a pair of coils. Write its SI unit. (ii) A long solenoid of radius R and length L has n turns per unit length. A circular loop of radius r(<R) is placed inside at the centre of the solenoid such that its axis coincides with the axis of the solenoid. Obtain the mutual inductance of the solenoid and the loop. OR Two long straight parallel conductors A and B carrying steady currents Ia and Ib in the same direction are separated by a distance d. Deduce the expressions for the force acting on length L of conductor B due to conductor A and show it in a figure. Write the expression for the force acting on length L of conductor A due to conductor B and show that it follows Newton's third law.

(a) State Bohr's second postulate and mention its significance. (b) Prove that, in Bohr model of hydrogen atom, as the principal quantum number n becomes large, the energy levels get closer and closer.

(a) Explain the statement: "Current is a scalar although we represent current with an arrow". (b) Use Kirchhoff's rules to find the current through the 3Ω resistor in the circuit shown in the figure.

Derive an expression for the magnetic field B, due to a circular coil of N turns, each of radius r carrying current I, at a distance x from the centre along its axis.

Case Study: A p-type or n-type semiconductor can be converted into a p-n junction by doping it with a suitable impurity. The motion of majority charge carriers causes diffusion current across the junction while the barrier electric field causes motion of minority carriers for drift current. In an unbiased diode, the diffusion and drift currents are equal. This equilibrium is disturbed by the biasing batteries. Diodes therefore allow currents in one direction. This property of a diode is used in making rectifiers. (i) Silicon is doped with which of the following to obtain a p-type semiconductor? (A) Phosphorus (B) Arsenic (C) Boron (D) Antimony (ii) A semiconductor has an electron concentration of 5×10²²m⁻³. The concentration of holes is (given nᵢ = 1.5×10¹⁶m⁻³) (A) 5×10²²m⁻³ (B) 1.5×10⁶m⁻³ (C) 9×10⁸m⁻³ (D) 4.5×10⁹m⁻³ (iii) During forward biasing of a p-n junction diode, the (A) current is mainly due to drifting of majority carriers. (B) current is mainly due to drifting of minority carriers. (C) diffusion and drift currents are equal. (D) current is of the order of 1A. (iv) (a) The threshold voltage for a silicon diode is about (A) 0.2V (B) 0.5V (C) 0.7V (D) 1.5V OR (iv) (b) When we dope Ge with a pentavalent element, four of its electrons bond with four germanium neighbours but the fifth electron remains weakly bound. The ionisation energy for this electron is about (A) 0.01eV (B) 0.05eV (C) 0.1eV (D) 0.15eV

Case Study: In an experiment with a convex lens of focal length f, the screen is fixed at a distance D from the object. A student slowly moves the lens away from the object towards the screen and finds that she is able to form a sharp image of the object for two positions of the lens. The distance between these two positions of the lens is d. (i) The value of d is (A) √(D(D-4f)) (B) √(D(D-2f)) (C) √(2Df) (D) √(D(D-f)) (ii) Compared to the size of the object, the images formed in the two positions of the lens are respectively (A) reduced, enlarged (B) reduced, reduced (C) enlarged, enlarged (D) enlarged, reduced (iii) If the distance between object and screen is 80.00cm and the lens forms sharp images at two positions separated by 20.00cm, the focal length of the convex lens is (A) 15.50cm (B) 18.75cm (C) 20.50cm (D) 22.75cm (iv) (a) Consider a convex lens of focal length 15cm. For which of the following values of object-screen distance can two positions of the object be found to obtain a sharp image on the screen? (A) 45cm (B) 50cm (C) 55cm (D) 65cm OR (iv) (b) A thin convex lens of focal length 10cm and another thin lens of focal length f are placed coaxially in contact. If the power of their combination is (10)/(3)D, the value of f is (A) -15cm (B) -10cm (C) -20cm (D) -30cm

(a) What are coherent sources? Why are they necessary for observing a stable interference pattern? Draw a graph showing the variation of intensity of light with the position on the screen in Young's double-slit experiment. (b) Find the intensity of light at a point on the screen when two interfering waves of the same intensity (I₀) have a path difference of (i) (λ)/(4) and (ii) (λ)/(3). OR (a) Draw a labelled ray diagram of a refracting telescope when it forms the image of a distant object at infinity. Derive an expression for its magnifying power. (b) (i) In a telescope the objective has a much larger aperture than the eyepiece. Why? (ii) Write two advantages of a reflecting telescope over a refracting telescope.

(a) Derive an expression for the capacitance of a parallel plate capacitor of plate area A and plate separation d with air present between the plates. (b) Two air-filled capacitors of capacitances C₁ and C₂ are connected in parallel with a dc battery. After the capacitors are fully charged, a slab of dielectric constant K is inserted between the plates of each capacitor. How will the (i) charge on each capacitor and (ii) energy stored in the capacitor be affected after the slab is introduced? OR (a) An electric field E is established across the ends of a cylindrical conductor of length L and area of cross-section A. Discuss how electrons attain an average velocity, independent of time. Hence obtain a relation between the current in the conductor and this average velocity of electrons. (b) (i) This average velocity is found to be a few mm/s for currents in the range of a few amperes. How then is current established almost the instant a circuit is closed? (ii) Two copper wires having their radii in the ratio 3:2 are connected in series across a battery. Find the ratio of the drift velocities of the electrons in the wires.

(a) A series combination of L, C and R is connected to an a.c. source. Using a phasor diagram, derive an expression for the impedance of the circuit and the phase difference between V and I. (b) Under what conditions is the (i) impedance of the circuit minimum? (ii) wattless current flowing in the circuit? OR (i) With the help of a labelled diagram, explain the principle, construction and working of an a.c. generator. (ii) Deduce an expression for the induced emf in the coil of the generator. (iii) If T is the time period of the rotation of the coil, at what values of T in a cycle is the emf of the generator maximum?