CBSE(NCERT) GRADE 12 PHYSICS 2025 SET3 — CBSE 12th Physics Previous Year Question Paper with Solutions

Q1 mcq 1 mark

The electric field (E) and electric potential (V) at a point inside a charged hollow metallic sphere are respectively :

A. E = 0, V = 0
B. E = 0, V = V0 (a constant)
C. E ≠ 0, V ≠ 0
D. E = E0 (a constant), V = 0

Solution hidden

Q3 mcq 1 mark

In a circular loop of radius R, current I enters at point A and exits at point B, as shown in the figure. The value of the magnetic field at the centre O of the loop is :

A. (A)
B. zero
C. (C)
D. (D)

Solution hidden

Q4 mcq 1 mark

The frequency of a photon of energy 1·326 eV is :

A. 1·18 × 10^14 Hz
B. 3·20 × 10^14 Hz
C. 4·20 × 10^15 Hz
D. 4·80 × 10^15 Hz

Solution hidden

Q5 mcq 1 mark

A metal rod of length 50 cm is held vertically and moved with a velocity field at the place is 0·4 G. The emf induced across the ends of the rod is :

A. 0·1 mV
B. 0·2 mV
C. 0·8 mV
D. 1·6 mV

Solution hidden

Q6 mcq 1 mark

Germanium crystal is doped at room temperature with a minute quantity of boron. The charge carriers in the doped semiconductors will be :

A. electrons only
B. holes only
C. holes and few electrons
D. electrons and few holes

Solution hidden

Q7 mcq 1 mark

The effective resistance between points A and B in the given circuit is :

A. 6
B. (B)
C. (C)
D. 2

Solution hidden

Q8 mcq 1 mark

A capacitor and an inductor are connected in series across an ac source of voltage of variable frequency. The frequency is increased continuously. The nature of the circuit before and after the resonance will be :

A. inductive only
B. capacitive only
C. capacitive and inductive respectively
D. inductive and capacitive respectively

Solution hidden

Q9 mcq

An alternating current is given by I = I0 cos (100)t. The least time the current takes to decrease from its maximum value to zero will be :

A. s
B. s
C. s
D. s

Solution hidden

Q10 mcq

The mass numbers of two nuclei A and B are 27 and 64 respectively. The ratio of their radii will be :

A. 3:4
B. 4:3
C. 27:64
D. 9:16

Solution hidden

Q11 mcq

Isotones are the nuclides having :

A. same mass numbers
B. same atomic numbers
C. same neutron number, but different atomic number
D. different neutron number, and different mass number

Solution hidden

Q12 mcq

A p-n junction diode is forward biased. As a result,

A. both the potential barrier height and the width of depletion layer decrease.
B. both the potential barrier height and the width of depletion layer increase.
C. the potential barrier height decreases and the width of depletion layer increases.
D. the potential barrier height increases and the width of depletion layer decreases.

Solution hidden

Q13 mcq

Assertion (A) : A ray of light is incident normally on the face of a prism. The emergent ray will graze along the opposite face of the prism when the critical angle at glass-air interface is equal to the angle of the prism. Reason (R) : The refractive index of a prism depends on angle of the prism.

A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
C. Assertion (A) is true, but Reason (R) is false.
D. Both Assertion (A) and Reason (R) are false.

Solution hidden

Q14 mcq

Assertion (A) : A charged particle is moving with velocity v in x-y plane, making an angle (0 < < ) with x-axis. If a uniform magnetic field is applied in the region, along y-axis, the particle will move in a helical path with its axis parallel to x-axis. Reason (R) : The direction of the magnetic force acting on a charged particle moving in a magnetic field is along the velocity of the particle.

A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
C. Assertion (A) is true, but Reason (R) is false.
D. Both Assertion (A) and Reason (R) are false.

Solution hidden

Q15 mcq

Assertion (A) : The minimum negative potential applied to the anode in a photoelectric experiment at which photoelectric current becomes zero, is called cut-off voltage. Reason (R) : The threshold frequency for a metal is the minimum frequency of incident radiation below which emission of photoelectrons does not take place.

A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
C. Assertion (A) is true, but Reason (R) is false.
D. Both Assertion (A) and Reason (R) are false.

Solution hidden

Q16 mcq

Assertion (A) : EM waves do not require a medium for their propagation. Reason (R) : EM waves are transverse waves.

A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
C. Assertion (A) is true, but Reason (R) is false.
D. Both Assertion (A) and Reason (R) are false.

Solution hidden

Q17 short answer 2 marks

Two wires made of the same material have the same length (l) but different cross-sectional areas A1 and A2. They are connected together with a cell of voltage V. Find the ratio of the drift velocities of free electrons in the two wires when they are joined in (i) series, and (ii) parallel.

Solution hidden

Q18 short answer 2 marks

Draw energy band diagrams of n-type and p-type semiconductors at temperature T > 0 K. Show the donor/acceptor energy levels with the order of difference of their energies from the bands.

Solution hidden

Q19 short answer 2 marks

The ratio of the widths of two slits in Young's double-slit experiment is 25 : 9. Calculate the ratio of intensities of the interfering waves.

Solution hidden

Q19 short answer 2 marks

In a Young's double-slit experiment, the ratio of widths of two slits is 25 : 9. Calculate the ratio of intensities of the interfering waves.

Solution hidden

Q20 short answer 2 marks

(a) Using the mirror equation and the formula of magnification, show that a concave mirror can produce an image which is always diminished in size and is located between the pole and the focus. OR (b) A convex lens of focal length 10 cm, a concave lens of focal length 15 cm and a third lens of unknown focal length are placed coaxially in contact. If the focal length of the combination is +12 cm, find the nature and focal length of the third lens, if all lenses are thin. Will the answer change if the lenses were thick?

Solution hidden

Q21 short answer 2 marks

Calculate the binding energy per nucleon (in MeV) of a helium nucleus. Given: m = 4·002603 u, mn = 1·008665 u, mH = 1·007825 u, 1 u = 931·5 MeV/c2.

Solution hidden

Q22 long answer 3 marks

State the Bohr's postulates for the hydrogen atom. Using them prove that, for an electron revolving in the nth orbit, (a) the radius of the orbit is proportional to n^2, and (b) the total energy of the atom is proportional to 1/n^2.

Solution hidden

Q23 long answer 3 marks

Four metals with their work functions are listed below: K = 2·3 eV, Na = 2·75 eV, Mo = 4·17 eV and Ni = 5·15 eV. The radiation of wavelength 330 nm from a laser source placed 1 m away, falls on these metals. Which of these metals will not show photoelectric emission? What will happen if the laser source is brought closer to a distance of 50 cm?

Solution hidden

Q24 long answer 3 marks

(a) (i) Write Biot-Savart law. (ii) Two identical circular coils A and B, each of radius R, carrying currents I and I respectively, are placed concentrically in XY and YZ planes respectively. Find the magnitude and direction of the net magnetic field at their common centre. OR (b) (i) A rectangular loop of sides l and b carries a current I clockwise. Write the magnetic moment of the loop and show its direction in a diagram. (ii) The loop is placed in a uniform magnetic field and is free to rotate about an axis which is perpendicular to the field. Prove that the loop experiences no net force, but a torque τ = m x B.

Solution hidden

Q25 long answer 3 marks

(a) How are electromagnetic waves produced? (b) Write the wavelength range and one use of: (i) Microwaves, and (ii) Ultraviolet waves.

Solution hidden

Q26 long answer 3 marks

(a) Two concentric circular coils of radii r1 and r2 (r2 >> r1) are placed coaxially with their centres coinciding. If a current I is passed through the outer coil, obtain the expression for mutual inductance of the arrangement. (b) The current in a solenoid decreases steadily from 6 mA to 2 mA in 50 ms. If an average emf of 0·4 V is induced, find the self-inductance of the solenoid.

Solution hidden

Q27 long answer 3 marks

Explain the formation of depletion region in a p-n junction region of a diode, with the help of a suitable diagram. Which feature of junction diode makes it suitable for its use as a rectifier?

Solution hidden

Q28 long answer 3 marks

Two point charges of 5 C and 2 C are located in free space at (-4 cm, 0) and (6 cm, 0) respectively. (a) Calculate the amount of work done to separate the two charges at infinite distance. (b) If this system of charges was initially kept in an electric field E = A(1/x^2)i, where A = 8 * 10^4 N C^-1 m^2, calculate the electrostatic potential energy of the system.

Solution hidden

Reading Passage

Q29 short answer

Solution hidden

Reading Passage

When light travels from an optically denser medium to an optically rarer medium, at the interface it is partly reflected back into the same medium and partly refracted to the second medium. The angle of incidence corresponding to an angle of refraction 90 is called the critical angle (ic) for the given pair of media. This angle is related to the refractive index of medium 1 with respect to medium 2. Refraction of light through a prism involves refraction at two plane interfaces. A relation for the refractive index of the material of the prism can be obtained in terms of the refracting angle of the prism and the angle of minimum deviation. For a thin prism, this relation reduces to a simple equation. Laws of refraction are also valid for refraction of light at a spherical interface. When an object is placed in front of a spherical surface separating two media, its image is formed. A relation between object and image distance, in terms of refractive indices of two media and the radius of curvature of the spherical surface can be obtained. Using this relation

Q30 mcq 1 mark

A small bulb is placed at the bottom of a tank containing a transparent liquid (refractive index n) to a depth H. The radius of the circular area of the surface of liquid, through which light from the bulb can emerge out, is R. Then is :

A. R = H / sqrt(n^2 - 1)
B. R = H * sqrt(n^2 - 1)
C. R = H / sqrt(n^2 + 1)
D. R = H * sqrt(n^2 + 1)

Solution hidden

Q31 mcq 1 mark

A parallel beam of light is incident on a face of a prism with refracting angle 60 . The angle of minimum deviation is found to be 30 . The refractive index of the material of the prism is close to :

A. 1.3
B. 1.4
C. 1.5
D. 1.6

Solution hidden

Q32 mcq 1 mark

The angle of minimum deviation for a ray of light incident on a thin prism, made of crown glass (n = 1.52) is Dm. If the prism was made of dense flint glass (n = 1.62) instead of crown glass, the angle of minimum deviation will :

A. decrease by 4%
B. increase by 4%
C. decrease by 19%
D. increase by 19%

Solution hidden

Q33 mcq 1 mark

An object is placed in front of a convex spherical glass surface (n = 1.5 and radius of curvature R) at a distance of 4R from it. As the object is moved slowly close to the surface, the image formed is :

A. always real
B. always virtual
C. first real and then virtual
D. first virtual and then real

Solution hidden

Q34 mcq 1 mark

A double-convex lens, made of glass of refractive index 1.5, has focal length 10 cm. The radius of curvature of its each face, is :

A. 10 cm
B. 15 cm
C. 20 cm
D. 40 cm

Solution hidden

Reading Passage

In a metallic conductor, an electron, moving due to thermal motion, suffers collisions with the heavy fixed ions but after collision, it will emerge out with the same speed but in random directions. If we consider all the electrons, their average velocity will be zero. When an electric field is applied, electrons move with an average velocity, known as drift velocity (vd). The average time between successive collisions is known as relaxation time (tau). The magnitude of drift velocity per unit electric field is called mobility (mu). An expression for current through the conductor can be obtained in terms of drift velocity, number of electrons per unit volume (n), electronic charge (e), and the cross-sectional area (A) of the conductor. This expression leads to an expression between current density (J) and the electric field (E). Hence, an expression for resistivity (rho) of a metal is obtained. This expression helps us to understand increase in resistivity of a metal with increase in its temperature, in terms of change in the relaxation time (tau) and change in the number density of electrons (n).

Q35 mcq 1 mark

Consider two cylindrical conductors A and B, made of the same metal connected in series to a battery. The length and the radius of B are twice that of A. If A and B are the mobility of electrons in A and B respectively, then ratio of drift velocity in A and B is :

A. 1
B. 4
C. 2
D. 1/2

Solution hidden

Q36 mcq 1 mark

A metallic conductor of length 0.5 m and cross-sectional area 1.0 x 10^-7 m^2 is connected to a DC battery of 2 V. If the current flowing through the conductor is 1.5 A, then the resistivity of the metal is (in ohm-meter) :

A. 2.5 x 10^4
B. 3.0 x 10^5
C. 3.75 x 10^6
D. 5.0 x 10^7

Solution hidden

Reading Passage

sion, it will emerge out with the same speed but in random directions. If we consider all the electrons, their average velocity will be zero. When an electric field is applied, electrons move with an average velocity, known as drift velocity (vd). The average time between successive collisions is known as relaxation time (τ). The magnitude of drift velocity per unit electric field is called mobility (μ). An expression for current through the conductor can be obtained in terms of drift velocity, number of electrons per unit volume (n), electronic charge (e), and the cross-sectional area (A) of the conductor. This expression leads to an expression between current density (J) and the electric field (E). Hence, an expression for resistivity (ρ) of a metal is obtained. This expression helps us to understand increase in resistivity of a metal with increase in its temperature, in terms of change in the relaxation time (τ) and change in the number density of electrons (n).

Q37 mcq 1 mark

A wire of length 0·5 m and cross-sectional area 1·0 × 10⁻⁷ m² is connected to a battery of 2 V that maintains a current of 1·5 A in it. The conductivity of the material of the wire (in Ω⁻¹ m⁻¹) is :

A. 2·5 × 10⁴
B. 3·0 × 10⁵
C. 3·75 × 10⁶
D. 5·0 × 10⁷

Solution hidden

Q38 mcq 1 mark

The temperature coefficient of resistance of nichrome is 1·70 × 10⁻⁴ ºC⁻¹. In order to increase resistance of a nichrome wire by 8·5%, the temperature of the wire should be increased by :

A. 250 ºC
B. 500 ºC
C. 850 ºC
D. 1000 ºC

Solution hidden

Q39 mcq 1 mark

Consider the contribution of the following two factors I and II in resistivity of a metal : I. Relaxation time of electrons II. Number of electrons per unit volume. The resistivity of a metal increases with increase in its temperature because :

A. I decreases and II increases.
B. I increases and II is almost constant.
C. Both I and II increase.
D. I decreases and II is almost constant.

Solution hidden

Q40 mcq 1 mark

A steady current flows in a copper wire of non-uniform cross-section. Consider the following three physical quantities : I. Electric field II. Current density III. Drift speed. Then at the different points along the wire :

A. II and III change, but I is constant.
B. I and II change, but III is constant.
C. I and III change, but II is constant.
D. All I, II and III change.

Solution hidden

Q41 long answer 5 marks

Explain with the help of a labelled ray diagram the formation of final image by an astronomical telescope at infinity. Write the expression for its magnifying power.

Solution hidden

Q42 long answer 5 marks

The total magnification produced by a compound microscope is 20. The magnification produced by the eyepiece is 5. When the microscope is focussed on a certain object, the distance between the objective and eyepiece is observed to be 14 cm. Calculate the focal lengths of the objective and the eyepiece. (Given that the least distance of distinct vision = 25 cm)

Solution hidden

Q43 long answer 5 marks

Two coherent light waves, each of intensity I0 superpose each other and produce interference pattern on a screen. Obtain the expression for the resultant intensity at a point where the phase difference between the waves is φ. Write its maximum and minimum possible values.

Solution hidden

Q44 long answer 5 marks

In a single slit diffraction experiment, the aperture of the slit is 3 mm and the separation between the slit and the screen is 1·5 m. A monochromatic light of wavelength 600 nm is normally incident on the slit. Calculate the distance of (I) first order minimum, and (II) second order maximum, from the centre of the screen.

Solution hidden

Q45 long answer 5 marks

A parallel plate capacitor with plate area A and plate separation d has a capacitance C0. A slab of dielectric constant K having area A and thickness t is inserted in the capacitor, parallel to the plates. Find the new value of its capacitance.

Solution hidden

Q46 long answer 5 marks

You are provided with a large number of 1µF identical capacitors and a power supply of 1200 V. The dielectric medium used in each capacitor can withstand up to 200 V only. Find the minimum number of capacitors and their arrangement, required to build a capacitor system of equivalent capacitance of 2 µF for use with this supply.

Solution hidden

Q47 long answer 5 marks

An electric dipole of dipole moment p consists of point charges q and -q, separated by 2a. Derive an expression for electric potential in terms of its dipole moment at a point at a distance x (>> a) from its centre and lying (I) along its axis, and (II) along its bisector line.

Solution hidden

Q48 long answer 5 marks

An electric dipole of dipole moment p = (0·8 i + 0·6 j) * 10^-29 Cm is placed in an electric field E = 1·0 * 10^7 i. Calculate the magnitude of the torque acting on it and the angle it makes with the x-axis, at this instant.

Solution hidden

Q49 long answer 5 marks

With the help of a labelled diagram, explain the principle of working of a moving coil galvanometer. Write the purpose of using (i) radial magnetic field, and (ii) soft iron core, in it.

Solution hidden

Q50 long answer 5 marks

Explain why increasing current sensitivity may not necessarily increase the voltage sensitivity.

Solution hidden

Q51 long answer 5 marks

State the Biot-Savart law and explain the terms used.

Solution hidden

Q52 long answer 5 marks

As the current carrying solenoid is made longer, the magnetic field produced outside it approaches zero. Why?

Solution hidden

Q53 long answer 5 marks

A flexible loop of irregular shape carrying current when located in an external magnetic field, changes to a circular shape. Give reason.

Solution hidden

Q54 long answer 5 marks

A galvanometer of resistance G is converted into a voltmeter to measure up to V volts, by connecting a resistance R1 in series with the coil. If R1 is replaced by R2, then it can only measure up to V/2 volt. Find the value of the resistance R3 (in terms of R1 and R2) needed to convert it into a voltmeter that can read up to 2V.

Solution hidden