List of top Questions asked in CBSE CLASS XII- 2025

Rani, Maharani and Laxmi were partners in a firm sharing profits and losses in the ratio of 3 : 3 : 2. On 1stApril, 2024 they admitted Reena as a new partner for \( \frac{1}{5} \) share in the profits of the firm. Reena acquired her share from Rani and Maharani in the ratio of 3 : 2. The new profit sharing ratio between Rani, Maharani, Laxmi and Reena will be :
A system of two conductors is placed in air and they have net charge of \( +80 \, \mu C \) and \( -80 \, \mu C \) which causes a potential difference of 16 V between them.
(1) Find the capacitance of the system.
(2) If the air between the capacitor is replaced by a dielectric medium of dielectric constant 3, what will be the potential difference between the two conductors?
(3) If the charges on two conductors are changed to +160µC and −160µC, will the capacitance of the system change? Give reason for your answer.
Two statements are given one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
Assertion (A): X-rays are produced when slow moving electrons are stopped by a metal target of high atomic number.
Reason (R): X-rays consist of low-energy photons.
4,000 shares of ₹ 10 each were forfeited for non-payment of second and final call money of ₹ 2 per share. The minimum amount that the company must collect at the time of reissue of these shares will be :
Draw a ray diagram showing the image formation when a concave mirror produces a real, inverted, and magnified image of an object and hence obtain the mirror formula.
Two statements are given one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C) and (D) as given below.
Assertion (A): A hole is an apparent free particle with effective positive electronic charge.
Reason (R): A hole is not necessarily a vacancy left behind by an electron in the valence band.
A current flows through a cylindrical conductor of radius \( R \). The current density at a point in the conductor is \( j = \alpha r \) (along its axis), where \( \alpha \) is a constant and \( r \) is the distance from the axis of the conductor. The current flowing through the portion of the conductor from \( r = 0 \) to \( r = \frac{R}{2} \) is proportional to:
Assertion (A): EM waves do not require a medium for their propagation.
Reason (R): EM waves are transverse waves.
Write vector form of Biot–Savart law.

An ideal transformer is designed to convert 50 V into 250 V. It draws 200 W power from an AC source whose instantaneous voltage is given by \( v_i = 20 \sin(100\pi t) \, \text{V} \).

Find:

  • 1. RMS value of input current.
  • 2. Expression for instantaneous output voltage.
  • 3. Expression for instantaneous output current.
Two coils ‘1’ and ‘2’ are placed close to each other as shown in the figure. Find the direction of induced current in coil ‘1’ in each of the following situations, justifying your answers:
Two coils ‘1’ and ‘2’ are placed

(a) Coil ‘2’ is moving towards coil ‘1’.
(b) Coil ‘2’ is moving away from coil ‘1’.
(c) The resistance connected with coil ‘2’ is increased keeping both the coils stationary.
Two small solid metal balls A and B of radii \(R\) and \(2R\) having charge densities 2 and 3 respectively are kept far apart. Find the charge densities on A and B after they are connected by a conducting wire.
A cell of emf \( E \) and internal resistance \( r \) is connected to an external variable resistance \( R \). Plot a graph showing the variation of terminal voltage \( V \) of the cell as a function of current \( I \), supplied by the cell. Explain how the emf of the cell and its internal resistance can be found from it.
Current I (= 1 A) is passing through a copper rod (n = \(8.5 \times 10^{28} \, \text{m}^{-3}\)) of varying cross-sections as shown in the figure. The areas of cross-section at points A and B along its length are \(1.0 \times 10^{-7} \, \text{m}^2\) and \(2.0 \times 10^{-7} \, \text{m}^2\) respectively. Calculate:
Current I (= 1 A) is passing through a copper rod
(I) the ratio of electric fields at points A and B.
(II) the drift velocity of free electrons at point B.
If \( R_s \) and \( R_p \) are the equivalent resistances of \( n \) resistors, each of value \( R \), in series and parallel combinations respectively, then the value of \( (R_s - R_p) \) is:
Diksha Ltd. invited applications for issuing 1,00,000 equity shares of ₹ 10 each at a premium of 10%. The whole amount was payable on application. Applications were received for 3,00,000 equity shares. The company decided to allot the shares on pro-rata basis to all the applicants. The amount refunded by the company was:
Germanium crystal is doped at room temperature with a minute quantity of boron. The charge carriers in the doped semiconductor will be:
A deuteron contains a proton and a neutron and has a mass of 2.013553 u. Calculate the mass defect for it in u and its energy equivalence in MeV.
Given:
\( m_p = 1.007277 \) u, \( m_n = 1.008665 \) u, \( 1 \) u = \( 931.5 \) MeV/\( c^2 \).
_____ are the colours, that represent the four regional confederation in the Deaflympic logo.
State Kirchhoff’s laws. Apply these laws to find the values of current flowing in the three branches of the given circuit.
Kirchhoff’s laws.
A current of 5 A is passing along +X direction through a wire lying along X-axis. Find the magnetic field \( \vec{B} \) at a point \( \vec{r} = (3 \hat{i} + 4 \hat{j}) \, \text{m} \) due to 1 cm element of the wire, centered at the origin.
The frequency of a photon of energy 1.326eV is:
The kinetic energy of an alpha particle is four times the kinetic energy of a proton. The ratio \( \left( \frac{\lambda_\alpha}{\lambda_p} \right) \) of de Broglie wavelengths associated with them will be:
Using the mirror equation and the formula of magnification, deduce that “the virtual image produced by a convex mirror is always diminished in size and is located between the pole and the focus.”
Define the term, ‘distance of closest approach’. A proton of 3.95 MeV energy approaches a target nucleus \( Z = 79 \) in head-on position. Calculate its distance of closest approach.