CBSE Class 12 Physics Guess Paper 2027

[case context: moving coil galvanometer conversion.] A galvanometer with coil of resistance 20 ohm shows full scale deflection for a current of 5 mA. To convert it into an ammeter of range (0 – 10 A), a resistance of (A) 0.05 ohm should be connected in series with it. (B) 0.05 ohm should be connected in parallel with it. (C) 0.01 ohm should be connected in parallel with it. (D) 0.01 ohm should be connected in series with it.

The following graph shows the potential difference across the terminals of a cell against its load current. [graph: potential difference (V) versus load current (A)] Find, (I) the emf of the cell and (II) the internal resistance of the cell. [For VI candidates: Find the relation between internal resistance, emf, external resistance and the total current in the circuit?]

The ratio of the nuclear densities of two nuclei having the mass numbers 8 and 27 is (A) 8:27 (B) 3:2 (C) 2:3 (D) 1:1

The 'distance of closest approach' of an alpha-particle is 'd' when it moves with a velocity v head-on towards the target nucleus. If the velocity of alpha particle is halved, the new 'distance of closest approach' will be (A) d/2 (B) 2d (C) d/4 (D) 4d

Which of the following figures correctly represent the shape of curve of binding energy per nucleon as a function of mass number? (Options A, B, C, D show different curves of B.E./A versus mass number A.)

In an unbiased p-n junction, at equilibrium, which of the following statements is true? (A) Diffusion current is zero but drift current exists. (B) Diffusion current exists but drift current is zero. (C) Diffusion and drift currents are equal and opposite. (D) Both the diffusion and drift currents exist but are unequal.

The diffraction effect can be observed in (A) sound waves only (B) light waves only (C) ultrasonic waves only (D) sound waves as well as light waves

Four independent waves are expressed as (i) y₁ = A₁ sin omega t (ii) y₂ = A₂ sin 2 omega t (iii) y₃ = A₃ cos omega t (iv) y₄ = A₄ sin(omega t + pi/3). The interference between two of these waves is possible in (A) (i) and (iii) only (B) (iii) and (iv) only (C) (i), (iii) and (iv) only (D) All of them

Which of the following statement is true for the radio waves and the gamma rays? (A) The energy of gamma rays is lesser than that of the radio waves. (B) The frequency of the radio waves is higher than that of gamma rays. (C) The radio waves and the gamma rays have the same energy. (D) The energy of radio waves is lesser than that of the gamma rays.

A long straight wire of circular cross-section (radius a) carries a steady current I. The current is uniformly distributed across this cross-section. The magnitude of the magnetic field produced at a point at a distance (a/2) from the axis of the wire will be (A) Zero (B) mu₀ I/(2 pi a) (C) mu₀ I/(4 pi a) (D) mu₀ I/(6 pi a)

A conducting wire connects two charged metallic spheres A and B of radii r₁ and r₂ respectively. The distance between the spheres is very large compared to their radii. The ratio of electric fields, (E_A/E_B) at the surfaces of spheres A and B will be (A) r₁/r₂ (B) r₂/r₁ (C) r₁²/r₂² (D) r₂²/r₁²

In a series LCR circuit, the voltage across the resistor, capacitor and inductor is 10 V each. If the capacitor is short circuited, the voltage across the inductor will be (A) 10 V (B) 5√2 V (C) 5/√2 V (D) 10√2 V

Assertion (A): In Bohr model of hydrogen atom, the energy levels are discrete and quantised. Reason (R): In a hydrogen atom, the electrostatic force on the electron provides the necessary centripetal force to it to revolve around the nucleus. [Standard assertion-reason options: (A) both true, R correct explanation; (B) both true, R not correct explanation; (C) A true, R false; (D) both false]

Assertion (A): If accelerated electrons are passed through a narrow slit, a diffraction pattern is observed. Reason (R): Electrons behave as both particles and waves. [Standard assertion-reason options: (A) both true, R correct explanation; (B) both true, R not correct explanation; (C) A true, R false; (D) both false]

Draw a diagram representing the behaviour of magnetic field lines for (A) diamagnetic & (B) paramagnetic substance. [For VI-Candidates: State Gauss's law of magnetism? Hence find the magnetic flux linked with the sphere enclosing a current carrying solenoid?]

Assertion (A): The critical angle of light passing from glass to air is minimum for violet colour. Reason (R): The wavelength of blue light is greater than the light of other colours.

In a photoelectric experiment, the emitter plate is irradiated with radiation of 200 nm. The photocurrent becomes zero when the collector plate potential is −0.80 V. Calculate the work function (in eV) of the emitter.

In a Young's double-slit experimental set-up with slit separation 0.6 mm a beam of light consisting of two wavelengths 440 nm and 660 nm is used to obtain interference pattern on a screen kept 1.5 m in front of the slits. Find the least distance of the point from the central maximum where the bright fringes due to both the wavelengths coincide.

In a Young's double-slit experiment, two light waves, each of intensity I₀, interfere at a point, having a path difference lambda/8 on the screen. Find the intensity at this point.

A transparent solid cylindrical rod (refractive index 2/sqrt(3)) is kept in air. A ray of light incident on its face travels along the surface of the rod, as shown in figure. Calculate the angle theta.

Write an expression for the magnetic force per unit length between two parallel thin current carrying wires. Hence define one ampere.

A compound microscope consists of an objective lens of focal length 0.82 cm and an eyepiece lens of focal length 2.9 cm. An object is placed 0.91 cm from the objective lens. The image is formed at the near point (25 cm) from the eye. (I) Calculate the angular magnification of the microscope. (II) Draw the ray diagram of compound microscope in normal adjustment.

(a) Obtain the condition of balance of a Wheatstone bridge. (b) Find net resistance of the network of resistors connected between A and B, as shown in figure.

(a) Draw the ray diagram to show the image formation by a refracting telescope and write the expression for angular magnification for the telescope in normal adjustment. (b) Give two reasons to explain why a reflecting telescope is preferred over a refracting telescope.

With the help of circuit diagram explain working of the full wave rectifier.

(A) A dielectric slab of thickness t, is introduced between the plates of parallel plate capacitor of area A and separation d (where t<d). Find an expression for the capacitance with the dielectric slab. (B) A copper sphere of capacitor C is dropped in ocean. Will the capacitance of the sphere increase, decrease or remain same? Justify. (C) A capacitor is connected across a source of potential difference V and then the separation 'd' between the plates is increased using insulating stick. Plot 'V' vs 'd' graph for the given capacitor. [For VI Candidates (C): A capacitor is connected across potential difference V and is then separation between plates 'd' is increased using insulating stick. Will the energy stored in capacitor increase or decrease? Justify]

(a) Using Gauss's law, deduce an expression for electric field at a point due to a uniformly charged infinite plane thin sheet. (b) Two large thin plane sheets, each having surface charge density sigma, are held close and parallel to each other in air. What is the net electric field at a point (i) inside and (ii) outside, the sheets?

(i) A conductor of length l is connected across an ideal cell of emf E. Keeping the cell connected, the length of the conductor is increased to 2l by gradually stretching it. If R and R' are initial and final values of resistance and v_d and v_d' are initial and final values of drift velocity, find the relation between (i) R' and R and (ii) v_d' and v_d. (ii) When electrons drift in a conductor from lower to higher potential, does it mean that all the 'free electrons' of the conductor are moving in the same direction?

[case context: forward/reverse biasing of a semiconductor diode — in forward bias p-side is at positive terminal and applied voltage drops mostly across the depletion region; in reverse bias n-side is positive] Ge and Si diodes start conducting at 0.3 V and 0.7 V respectively. In the following figure if Ge diode connection are reversed, the value of V₀ changes by (assume that the Ge diode has large breakdown voltage) [circuit: 12 V source, Ge and Si diodes in parallel, 5 K resistor] (A) 0.2 V (B) 0.4 V (C) 0.6 V (D) 0.8 V

[case context: photoelectric effect apparatus with emitter C, collector A, terminal B and microammeter] In the given diagram, if terminal B is shifted towards the left then how will it affect the reading of the microammeter? [for V.I. candidates: If the supplied voltage is decreased, then what will be effect on the reading of the microammeter?]

(a) Draw a labelled diagram of a step-up transformer. State the principle on which it works and obtain the ratio of secondary voltage to primary voltage in terms of number of turns and currents in the two coils. (b) The ratio of the number of turns in the primary to the secondary of an ideal transformer is 1 : 5. If 5 kW power at 200 V is supplied to the primary, find (i) current in the primary, and (ii) output voltage.

(a) Using the relation for refraction at a curved spherical surface, derive the expression for lens maker's formula. (b) Three lenses L₁, L₂ and L₃, each of focal length 40 cm, are placed coaxially. The distance between L₁ and L₂ and between L₂ and L₃ are 120 cm and 20 cm respectively. An object is kept at a distance of 80 cm to the left of lens L₁. Find the distance of the final image formed from the object.

(A) Define angle of deviation in a prism? (B) Obtain the relation A+delta=i+e for a prism where A is the angle of prism, delta is the angle of deviation, i is the angle of incidence and e is the angle of emergence. Write this relation for the minimum deviation? (C) Write the condition for minimum deviation.