List of top Physics Questions asked in CBSE CLASS XII

Two parallel beams of protons moving in the same direction will:

A galvanometer having a coil resistance of \(48\,\Omega\) shows full-scale deflection for a current of \(2.0\) A. It can be converted into an ammeter of range \((0-10\,\text{A})\) by connecting:

In a Rutherford scattering experiment, when an alpha particle of mass \(m_1\) approaches a target nucleus of charge \(Ze\) and mass \(m_2\), the distance of the closest approach is \(d_0\). The energy of the particle is:

A rectangular loop \((1\,\text{cm} \times 5\,\text{cm})\) of wire carrying current of 0.4 A is placed in a magnetic field \(\vec{B} = (0.03\hat{i} + 0.04\hat{k})\) T such that the outward unit vector normal to the plane of the loop is \((0.60\hat{i} - 0.80\hat{j})\). Calculate: (a) the magnetic moment \(\vec{m}\) of the loop, and (b) the torque \(\vec{\tau}\) acting on the loop.

In a Young's double-slit experiment with light of wavelength 520 nm, the fringe width is 0.52 mm. What will be the fringe width if the entire apparatus is immersed in water (refractive index \(\dfrac{4}{3}\))?

What is thermonuclear fusion? Calculate the energy released in MeV in the fusion reaction given below:

\(^2_1\text{H} + {}^3_1\text{H} \longrightarrow {}^4_2\text{He} + n\)

Given: \(m(^2_1\text{H}) = 2.014102\) u, \(m(^3_1\text{H}) = 3.016049\) u, \(m(^4_2\text{He}) = 4.002603\) u, \(m_n = 1.008665\) u, 1 u = 930 MeV/c\(^2\).

Two cells are connected in parallel by connecting their positive terminals together and connecting their negative terminals together. Derive expression for the equivalent emf and the equivalent internal resistance of the combination.

Define electric field. Write its SI unit. A point charge \(q = 25\,\mu\text{C}\) is located at the point \((0, 0)\) in x-y plane. Find (i) the magnitude of electric field at point \((3\,\text{cm}, 4\,\text{cm})\), and (ii) the angle the field makes with the x-axis.

The electric field due to a uniformly and negatively charged thin spherical shell at a point outside the shell at a distance \(r\) from its centre is:

Two long, straight, parallel conductors carry the same current and attract each other with a force F per unit length. If the current is doubled in each conductor and their separation is made half, the force per unit length becomes:

An electron of mass m and charge e is accelerated from rest through a potential difference V. Prove that, after acceleration, the de Broglie wavelength associated with the electron is proportional to \(\dfrac{1}{\sqrt{V}}\).

Which of the following electromagnetic waves are known as 'heat waves'?

In Bohr model of the hydrogen atom, the kinetic energy of an electron in \(n = 2\) orbit is:

A circular loop of wire of radius 7.0 cm carrying a current of 1.0 A is placed in a magnetic field \(\vec{B} = (0.5\hat{i} + 0.4\hat{k})\) T such that the outward unit vector normal to the plane of the loop is \([0.60\hat{i} + 0.80\hat{j}]\). Calculate: (a) the magnetic moment \(\vec{m}\) of the loop, and (b) the torque \(\vec{\tau}\) acting on the loop. (Take \(\pi = \dfrac{22}{7}\))

Consider two long, straight, parallel conductors A and B separated by a distance \(d\). They carry steady current \(I\) in the same direction. The force acting on unit length of conductor B due to conductor A is:

In a Young's double-slit experiment with monochromatic light of wavelength 600 nm, and slit separation of 2 mm, fringes are observed on a screen at some distance. Calculate the change in fringe width if the screen is moved towards the slits by 10 cm.

Monochromatic light of frequency \(7.0 \times 10^{14}\) Hz is produced by a laser. The power emitted is 21 mW. Calculate (i) the energy of a photon in the light beam, and (ii) the number of photons per second, on an average, emitted by the source.

Define 'emf' of a cell. Derive expression for the equivalent emf and the equivalent internal resistance of two cells connected in series.

Give an example of fission reaction. Calculate the energy released by the fission of 1 kg of \(^{235}_{92}\text{U}\) in kWh. The energy released per fission is 200 MeV.

Write Coulomb's law in vector form. Two point charges \(q_1 = 10\,\mu\text{C}\) and \(q_2 = 20\,\mu\text{C}\) are located, respectively, in the x-y plane at points \((0, 0)\) and \((3\,\text{cm}, 4\,\text{cm})\). Find (i) the magnitude of the force exerted on \(q_2\) by \(q_1\), and (ii) the angle that the force makes with the x-axis.

In Bohr model of the hydrogen atom, the potential energy of electron in the ground state is:

The electric field due to an infinitely long, straight, uniformly and positively charged wire at a point at distance \(r\) from the wire is:

Welders wear special glass goggles or face masks with glass windows to protect their eyes from:

According to the band theory of solids, a semiconductor has a valence band and a conduction band separated by a gap, known as energy band gap. Pure semiconductors are called intrinsic semiconductors. At room temperature, some electrons from the valence band can acquire enough energy to cross the band gap and enter the conduction band. The number of conduction electrons is equal to the number of holes in an intrinsic semiconductor. The number of charge carriers can be changed by doping of a suitable impurity in a pure semiconductor. Such semiconductors are known as extrinsic semiconductors. These are of two types (n-type and p-type).

A p-n junction is the basic building block of semiconductor devices. Two important processes occur during formation of a p-n junction: diffusion and drift. A 'depletion layer' is formed in a p-n junction. This is responsible for a junction potential barrier. A semiconductor diode is basically a p-n junction with metallic contacts provided at the ends for the application of an external voltage. A diode can be forward-biased or reverse-biased. The barrier height and the depletion layer width in a p-n junction changes depending on the nature of the biasing.