List of top Physics Questions asked in CBSE CLASS XII

Which of the following statements about dielectrics is correct?
Which of the following is a polar molecule?
In a diode, the reverse current is practically not dependent on the applied voltage.
In a p-n junction under equilibrium, there is no net current.
A doped semiconductor is electrically neutral.
With the help of a circuit diagram, explain the working of a full wave rectifier.
Explain the characteristics of a p-n junction diode that makes it suitable for its use as a rectifier.
Write briefly one method each, of the production and detection of these radiations.
Name the parts of the electromagnetic spectrum which are absorbed by the ozone layer in the atmosphere.
(i) Name the parts of the electromagnetic spectrum which are also known as ‘heat waves’.
An electron moving with a velocity \( \vec{v} = (1.0 \times 10^7 \, \text{m/s}) \hat{i} + (0.5 \times 10^7 \, \text{m/s}) \hat{j} \) enters a region of uniform magnetic field \( \vec{B} = (0.5 \, \text{mT}) \hat{j} \). Find the radius of the circular path described by it. While rotating, does the electron trace a linear path too? If so, calculate the linear distance covered by it during the period of one revolution.}
Two long straight parallel wires separated by 20 cm carry 5 A and 10 A current respectively, in the same direction. Find the magnitude and direction of the net magnetic field at a point midway between them.
State and explain Ampere’s circuital law.
A metal rod of length 2 m is rotated with a frequency of 60 rev/s about an axis passing through its centre and perpendicular to its length. A uniform magnetic field of 2T perpendicular to its plane of rotation is switched-on in the region. Calculate the e.m.f. induced between the centre and the end of the rod.
State Lenz's Law. In a closed circuit, the induced current opposes the change in magnetic flux that produced it as per the law of conservation of energy. Justify.
A plane surface, in the shape of a square of side 1 cm, is placed in an electric field \( \vec{E} = (100 \, \text{N/C}) \hat{i \) such that the unit vector normal to the surface is given by \( \hat{n} = 0.8 \hat{i} + 0.6 \hat{k} \). Find the electric flux through the surface.}
Define the term 'electric flux' and write its dimensions.
Explain the existence of threshold frequency of incident radiation for photoelectric emission from a given surface.
Write Einstein’s photoelectric equation. How did Millikan prove the validity of this equation?
The Earth revolves around the Sun in an orbit of radius \(1.5 \times 10^{11} \, \text{m}\) with orbital speed \(30 \, \text{km/s}\). Find the quantum number that characterizes its revolution using Bohr’s model in this case (mass of Earth \( = 6.0 \times 10^{24} \, \text{kg}\)).
In which series of hydrogen spectrum does this line fall?
Two energy levels of an electron in a hydrogen atom are separated by 2.55 eV. Find the wavelength of radiation emitted when the electron makes a transition from the higher energy level to the lower energy level.
A telescope has an objective lens of focal length 150 cm and an eyepiece of focal length 5 cm. Calculate its magnifying power in normal adjustment and the distance of the image formed by the objective.
Derive an expression for magnetic force \( \vec{F} \) acting on a straight conductor of length \( L \) carrying current \( I \) in an external magnetic field \( \vec{B} \). Is it valid when the conductor is in zig-zag form? Justify.
Four point charges of 1 \(\mu C\), -2 \(\mu C\), 1 \(\mu C\), and -2 \(\mu C\) are placed at the corners A, B, C, and D respectively, of a square of side 30 cm. Find the net force acting on a charge of 4 \(\mu C\) placed at the center of the square.