Physics 55/5/1 2025-2026 Science (English Medium) Class 12 Question Paper Solution

Two small identical metallic balls having charges q and −2q are kept far at a separation r. They are brought in contact and then separated at distance `r/2`. Compared to the initial force F, they will now ______.

attract with a force `F/2`.

repel with a force `F/2`.

repel with a force F.

attract with a force F

The figure represents the variation of the electric potential V at a point in a region of space as a function of its position along the x-axis. A charged particle will experience the maximum force at ______.

P

Q

R

S

Four long straight thin wires are held vertically at the corners A, B, C and D of a square of side ‘a’, kept on a table and carry equal current T. The wire at A carries current in upward direction whereas the current in the remaining wires flows in downward direction. The net magnetic field at the centre of the square will have the magnitude ______.

`(mu_0 I)/(pi a)` and directed along OC.

`(mu_0 I)/(pi a sqrt 2)` and directed along OD.

`(mu_0 I sqrt2)/(pi a)` and directed along ОВ.

`(2 mu_0 I)/(pi a)` and directed along OA.

The magnetic flux through a loop placed in a magnetic field can be changed by changing ______.

area of the loop only.

the value of magnetic field only.

orientation of the loop in the magnetic field only.

any one or more of the factors given in (A), (B) and (C).

Which of the following statements is not true for electric energy in ac form compared to that in dc form?

Production of ac is economical.

ас сan be easily and efficiently converted from one voltage to the other.

ас can be transmitted economically over long distances.

ac is less dangerous.

The magnetic field in a plane electromagnetic wave travelling in glass (n = 1.5) is given by

B_y = (2 × 10⁻⁷ T) sin (αx + 1.5 × 10¹¹ t)

where x is in metres and t is in seconds. The value of α is ______.

0.5 × 10³ m⁻¹

6.0 × 10² m⁻¹

7.5 × 10² m⁻¹

1.5 × 10³ m⁻¹

Light of which of the following colours will have the maximum energy in a photon associated with it?

Red light

Yellow light

Green light

Blue light

Nuclides with the same number of neutrons are called ______.

Isobars

Isotones

Isotopes

Isomers

The radius of a nucleus of mass number 125 is ______.

6.0 fm

30 fm

72 fm

150 fm

The energy of an electron in an orbit in hydrogen atom is −3.4 eV. Its angular momentum in the orbit will be ______.

`(3 h)/(2 pi)`

`(2 h)/pi`

`h/pi`

`h/(2 pi)`

A good diode checked by a multimeter should indicate ______.

high resistance in reverse bias and a low resistance in forward bias.

high resistance in both forward bias and reverse bias.

low resistance in both reverse bias and forward bias.

high resistance in forward bias and low resistance in reverse bias.

The rms and the average value of an ac voltage V = V₀ sin ot volt over a cycle respectively will be ______.

`V_0/2, V_0/sqrt 2`

`V_0/pi, V_0/2`

`V_0/sqrt2`, 0

V₀, `V_0/sqrt 2`

Assertion (A): Induced emf produced in a coil will be more when the magnetic flux linked with the coil is more. 

Reason (R): Induced emf produced is directly proportional to the magnetic flux.

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

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

Assertion (A) is true, but Reason (R) is false.

Both Assertion (A) and Reason (R) are false.

Assertion (A): In Young’s double-slit experiment, the fringe width for dark and bright fringes is the same.

Reason (R): Fringe width is given by β = `(lambda D)/d`, where symbols have their usual meanings.

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

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

Assertion (A) is true, but Reason (R) is false.

Both Assertion (A) and Reason (R) are false.

Assertion (A): Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion.

Reason (R): For heavy nuclei, binding energy per nucleon increases with increasing Z while for light nuclei, it decreases with increasing Z.

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

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

Assertion (A) is true, but Reason (R) is false.

Both Assertion (A) and Reason (R) are false.

Assertion (A): Photoelectric effect is a spontaneous phenomenon.

Reason (R): According to the wave picture of radiation, an electron would take hours/days to absorb sufficient energy to overcome the work function and come out from a metal surface.

Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

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

Assertion (A) is true, but Reason (R) is false.

Both Assertion (A) and Reason (R) are false.

An electric iron rated 2.2 kW, 220 V is operated at 110 V supply. Find:

1. its resistance, and
2. heat produced by it in 10 minutes.

A current of 4.0 A flows through a wire of length 1 m and cross-sectional area 1.0 mm², when potential difference of 2 V is applied across its ends.

Calculate the resistivity of the material of the wire.

A plane circular coil is rotated about its vertical diameter with a constant angular speed ω in a uniform horizontal magnetic field. Initially the plane of the coil is parallel to the magnetic field. Draw plots showing the variation of the following physical quantities as a function of ωt, where t represents time elapsed:

1. Magnetic flux Φ linked with the coil, and
2. emf induced in the coil.

A tank is filled with a liquid to a height of 12.5 m. The apparent depth of a needle lying at the bottom of the tank is measured to be 9.0 m. Calculate the speed of light in the liquid.

Two thin lenses of focal length f₁ and f₂ are placed in contact with each other coaxially. Prove that the focal length f of the combination is given by f = `(f_1 f_2)/(f_1 + f_2)`.

Suppose a pure Si crystal has 5 × 10²⁸ atoms per m³. It is doped with 5 × 10²² atoms per m³ of Arsenic. Calculate majority and minority carrier concentration in the doped silicon.

(Given: n_i = 1.5 × 10¹⁶ m⁻³)

Two parallel plate capacitors X and Y are connected in series to a 6 V battery. They have the same plate area and same plate separation but capacitor X has air between its plates, whereas capacitor Y contains a material of dielectric constant 4.

1. Calculate the capacitances of X and Y, if the equivalent capacitance of the combination of X and Y is 4 µF.
2. Calculate the potential difference across the plates of X and Y.

Write the expression for the magnetic field due to a current element in vector form. Consider a 1 cm segment of a wire, centered at the origin, carrying a current of 10 A in positive x-direction. Calculate the magnetic field `vec B` at a point (1 m, 1 m, 0).

A long solenoid of length L and radius r₁ having N₁ turns is surrounded symmetrically by a coil of radius r₂ (> r₁) having N₂ turns (N₂ ≪ N₁) around its mid-point. Derive an expression for the mutual inductance of solenoid and coil. Is M₁₂ = M₂₁ valid in this case?

What is meant by displacement current?

Considering the case of charging of a capacitor, show that i_d = `(d phi_E)/dt`. What is the value of i_d for a conductor across which a constant voltage is applied?

Write any two characteristic features of nuclear forces?

If both the number of protons and the neutrons are conserved in each nuclear reaction, in what way is mass converted into energy (or vice versa) in a nuclear reaction? Explain.

Draw the number of scattered particles versus the scattering angle graph for scattering of alpha particles by a thin foil. Write two important conclusions that can be drawn from this plot.

If Bohr's quantization postulate (angular momentum = `(n h)/(2 pi)`) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why, then, do we never speak of quantization of orbits of planets around the Sun? Explain.

Photoemission of electrons occurs from a metal (Φ₀ = 1.96 eV) when light of frequency 64 × 10¹⁴ Hz is incident on it. Calculate:

1. Energy of a photon in the incident light,
2. The maximum kinetic energy of the emitted electrons, and
3. The stopping potential.

Draw the circuit diagram of a full wave rectifier. Explain its working showing its input and output waveforms.

1. The electric field `vec E` in the region between the plates is ______.    (1)
   1. `(2 xx 10^2 V/m)hat k`
   2. `-(2 xx 10^2 V/m)hat k`
   3. `(2 xx 10^4 V/m) hat k`
   4. `-(2 xx 10^4 V/m)hat k`
2. In the region between the plates, the electron moves with an acceleration `vec a` given by ______.    (1)
   1. `-(3.5 xx 10^15 ms^-2)hat k`
   2. `(3.5 xx 10^15 ms^-2)hat k`
   3. `(3.5 xx 10^13 ms^-2)hat i`
   4. `-(3.5 xx 10^13 ms^-2)hat i`
3. 
   
   1. Time interval during which an electron moves through the region between the plates is ______.    (1)
      1. 9.0 × 10⁻⁹ s
      2. 1.67 × 10⁻⁸ s
      3. 1.67 × 10⁻⁹ s
      4. 2.17 × 10⁻⁹ s
         OR
   2. The vertical displacement of the electron which travels through the region between the plates is ______.    (1)
      1. 10 mm
      2. 4.9 mm
      3. 5.9 mm
      4. 3.0 mm
4. Which one of the following is the path traced by the electron in between the two plates?    (1)
   
   
   1. a
   2. b
   3. c
   4. d

1. What property of light does this interference experiment demonstrate?    (1)
   1. Wave nature of light.
   2. Particle nature of light.
   3. Transverse nature of light.
   4. Both wave nature and transverse nature of light.
2. 
   
   1. The wavelength of light used in this experiment is ______.    (1)
      1. 720 nm
      2. 590 nm
      3. 480 nm
      4. 364 nm
         OR
   2. The fringe width in the interference pattern formed on the screen is ______.
      1. 1.2 mm
      2. 0.2 mm
      3. 4.2 mm
      4. 6.8 mm
3. The path difference between the two waves meeting at point P, where there is a minimum in the interference pattern is ______.    (1)
   1. 8.1 × 10−7 m
   2. 7.2 × 10−7 m
   3. 6.5 × 10−7 m
   4. 6.0 × 10−7 m
4. When the experiment is performed in a liquid of refractive index greater than 1, then fringe pattern will ______.    (1)
   1. disappear
   2. become blurred
   3. be widened
   4. be compressed

Determine the current in the 3 Ω branch of a Wheatstone Bridge in the circuit shown in the figure.

Consider a cylindrical conductor of length I and area of cross-section A. Current I is maintained in the conductor and electrons drift with velocity v_d `(|vec v_d| = (e|vec E|)/m tau)`,  (where symbols have their usual meanings). Show that the conductivity o of the material of the conductor is given by σ = `(n e^2)/m tau`.

The resistance of a metal wire at 20°C is 1.05 Ω and at 100°C is 1.38 Ω. Determine the temperature coefficient of resistivity of this metal.

A rectangular loop of sides a and b carrying current I is placed in a magnetic field `vec B` such that its area vector `vec A` makes an angle θ with `vec B`. With the help of a suitable diagram, show that the torque `vec tau` acting on the loop is given by `vec tau = vec m xx vec B`, where `vec m(= I vec A)` is the magnetic dipole moment of the loop.

A eirecular cóil of 100 turna and radius `(10/sqrt pi)` cm carrying current of 5.0 A is suspended vertically in a uniform horizontal magnetic field of 2.0 T. The field makes an angle 30° with the normal to the coil. Calculate:

1. the magnetic dipole moment of the coil, and
2. the magnitude of the counter torque that must be applied to prevent the coil from turning.

Derive an expression for the force `vec F` acting on a conductor of length L and area of cross-section A carrying current I and placed in a magnetic field `vec B`.