List of top Physics Questions asked in CBSE CLASS XII

When monochromatic light is incident on a surface separating two media, the refracted and reflected light both have the same frequency as the incident frequency but the wavelength of refracted light is different. Explain why.
Assertion : 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 \( Z \).
Assertion : In Young’s double-slit experiment, the fringe width for dark and bright fringes is the same.
Reason (R): Fringe width is given by \( \beta = \frac{\lambda D}{d} \), where symbols have their usual meanings.
Two points R and S are equidistant from two charges \( +Q \) and \( -2Q \). The work done in moving a charge \( -Q \) from point R to S is:
A charged particle is moving in a uniform magnetic field \( \vec{B} \) with a constant speed \( v \) in a circular path of radius \( r \). Which of the following graphs represents the variation of radius of the circle, with the magnitude of magnetic field \( \vec{B} \)?
What are de Broglie waves? Show that the wavelength of the electromagnetic radiation is equal to the de Broglie wavelength of its quantum (photon).
Differentiate between conduction current and displacement current. A capacitor is connected across a source providing time-dependent current. Explain how the total current at an instant is the sum of conduction current and displacement current in the circuit at that instant.
A point source, in air, is placed at a distance of 6 cm in front of a convex spherical surface (n = 1.5 and radius of curvature = 24 cm). Find the position and nature of the image formed.
A square loop of side 10 cm, free to rotate about a vertical axis coinciding with its one arm, is initially held perpendicular to a uniform horizontal magnetic field of 0.2 T. If it is rotated at the uniform speed of 60 rpm, find the emf induced in the loop.
The energy of an electron revolving in the nth orbit in Bohr model of hydrogen atom is proportional to:
Which of the following statements is not true for electric energy in ac form compared to that in dc form?
A charged particle of mass m having kinetic energy K passes undeflected through a region with electric field \(\vec{E}\) and magnetic field \(\vec{B}\) acting perpendicular to each other. The mass m of the particle will be:
An electron is moving with velocity \(v_0 \hat{i}\). If a uniform electric field \(\vec{E} = E_0 \hat{j}\) is set up in the region, the electron will:
The rms and the average value of an ac voltage \(V = V_0 \sin \omega t\) volt over a cycle respectively will be:
The energy of an electron in an orbit in hydrogen atom is -3.4 eV. Its angular momentum in the orbit will be:
With the help of a ray diagram, describe the construction and working of a compound microscope.
Write any two points of difference between interference pattern due to double-slit and diffraction pattern due to single-slit.
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 \( \vec{B} \).
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 \( \theta \) with \( \vec{B} \). With the help of a suitable diagram, show that the torque \( \vec{\tau} \) acting on the loop is given by \( \vec{\tau} = \vec{m} \times \vec{B} \), where \( \vec{m} (= I \vec{A}) \) is the magnetic dipole moment of the loop.

The electric potential (V ) and electric field (⃗ E) are closely related concepts in electrostatics. The electric field is a vector quantity that represents the force per unit charge at a given point in space, whereas electric potential is a scalar quantity that represents the potential energy per unit charge at a given point in space. Electric field and electric potential are related by the equation

i.e., electric field is the negative gradient of the electric potential. This means that electric field points in the direction of decreasing potential and its magnitude is the rate of change of potential with distance. The electric field is the force that drives a unit charge to move from higher potential region to lower potential region and electric potential difference between the two points determines the work done in moving a unit charge from one point to the other point.
A pair of square conducting plates having sides of length 0.05 m are arranged parallel to each other in the x–y plane. They are 0.01 m apart along the z-axis and are connected to a 200 V power supply as shown in the figure. An electron enters with a speed of 3 × 107 m s−1 horizontally and symmetrically in the space between the two plates. Neglect the effect of gravity on the electron.

In a Young’s double-slit experiment, the two slits behave as coherent sources. When coherent light waves superpose over each other they create an interference pattern of successive bright and dark regions due to constructive and destructive interference. Two slits 2 mm apart are illuminated by a source of monochromatic light and the interfer- ence pattern is observed on a screen 5.0 m away from the slits as shown in the figure.

A point charge of 20 nC is fixed at the origin of x-y plane. The work done in taking a second point charge of \(-50\) nC from point \((4\,\text{cm}, 0)\) to point \((0, 5\,\text{cm})\) is:

A point charge of 10 nC is fixed at the origin of x-y plane. A second point charge of \(-20\) nC is moved from point \((5\,\text{cm}, 0)\) to point \((0, 5\,\text{cm})\). The change in the potential energy of the system of the two charges is:

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

Two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer from the options below:

(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.

Assertion (A): In process of photoelectric emission using a monochromatic light, all emitted electrons do not have the same kinetic energy.

Reason (R): If radiation falling on a photosensitive surface consists of different wavelengths, the energy of emitted photoelectrons by absorbing photons of different wavelengths, shall be different.