List of top Physics Questions asked in CBSE CLASS XII

A beam of light consisting of a known wavelength 520nm and an unknown wavelength λ, used in Young’s double slit experiment, produces two interference patterns such that the fourth bright fringe of unknown wavelength coincides with the fifth bright fringe of known wavelength. Find the value of λ
A step-up transformer converts a low voltage into high voltage. Does it violate the principle of conservation of energy? Explain.
(i) Draw a labelled diagram of a step-up transformer and describe its working principle. Explain any three causes for energy losses in a real transformer.
(ii) A step-up transformer converts a low voltage into high voltage. Does it violate the principle of conservation of energy? Explain.
(iii) A step-up transformer has 200 and 3000 turns in its primary and secondary coils respectively. The input voltage given to the primary coil is 90V. Calculate:
1. The output voltage across the secondary coil.
2. The current in the primary coil if the current in the secondary coil is 2.0A.
When does an inductor act as a conductor in a circuit? Give reason for it.
An electric dipole (dipole moment $\vec{p} = p \, \hat{i}$), consisting of charges $-q$ and $q$, separated by distance $2a$, is placed along the $x$-axis, with its center at the origin. Show that the potential $V$, due to this dipole, at a point $x$ ($x \gg a$) is equal to: \[ V = \frac{1}{4\pi\epsilon_0} \cdot \frac{\vec{p} \cdot \hat{i}}{x^2}. \]
In a full-wave rectifier:
An alternating voltage of frequency \( 50 \, \text{Hz} \) is applied to a half-wave rectifier. Then the ripple frequency of the output will be:
In a full-wave rectifier, the current in each of the diodes flows for:
A double-convex lens of power \( P \), with each face having the same radius of curvature, is cut along its principal axis. The two parts are arranged as shown in the figure. The power of the combination will be: \includegraphics[width=0.3\linewidth]{14image.png}
Two convex lenses of focal lengths \( 60 \, \text{cm} \) and \( 20 \, \text{cm} \) are held coaxially in contact with each other. The power of the combination is:
A double-convex lens, with each face having the same radius of curvature \( R \), is made of glass of refractive index \( n \). Its power is:
A double-convex lens of power \( P \), with each face having the same radius of curvature, is cut into two equal parts perpendicular to its principal axis. The power of one part of the lens will be:
Write the drawbacks of Rutherford’s atomic model. How did Bohr remove them? Show that different orbits in Bohr’s atom are not equally spaced.
A proton with kinetic energy $1.3384 \times 10^{-14 \, \text{J}$ moving horizontally from north to south, enters a uniform magnetic field $B = 2.0 \, \text{mT}$ directed eastward. Calculate:}
\textbf{(a) the speed of the proton,
An inductor, a capacitor, and a resistor are connected in series with an AC source \( v = v_m \sin \omega t \). Derive an expression for the average power dissipated in the circuit. Also, obtain the expression for the resonant frequency of the circuit.
"The wavelength of the electromagnetic wave is often correlated with the characteristic size of the system that radiates." Give two examples to justify this statement.
(i) Why do long-distance radio broadcasts use short-wave bands?
(ii) Why are optical and radio telescopes built on the ground, but X-ray astronomy is possible only from satellites orbiting the Earth?
Plot a graph showing the variation of current with voltage for the material GaAs. On the graph, mark the region where: \textbf{(a) resistance is negative, and
A cube of side $0.1 \, \text{m$ is placed, as shown in the figure, in a region where electric field $\vec{E} = 500x \, \hat{i}$ exists. Here $x$ is in meters and $E$ in $\text{N/C}$. Calculate:}
\textbf{(a) the flux passing through the cube, and
Define ‘current density’. Is it a scalar or a vector? An electric field $\vec{E$ is maintained in a metallic conductor. If $n$ be the number of electrons (mass $m$, charge $-e$) per unit volume in the conductor and $\tau$ its relaxation time, show that the current density $\vec{j} = \alpha \vec{E}$, where $\alpha = \left( \frac{ne^2}{m} \right) \tau$.}
What is a Wheatstone bridge? Obtain the necessary conditions under which the Wheatstone bridge is balanced.}
Monochromatic light of frequency $5.0 \times 10^{14 \, \text{Hz}$ passes from air into a medium of refractive index $1.5$. Find the wavelength of the light (i) reflected, and (ii) refracted at the interface of the two media.}
A plano-convex lens of focal length $16 \, \text{cm$ is made of a material of refractive index $1.4$. Calculate the radius of the curved surface of the lens.}
An object is placed 30 cm in front of a concave mirror of radius of curvature 40 cm. Find the (i) position of the image formed and (ii) magnification of the image.
Find the temperature at which the resistance of a wire made of silver will be twice its resistance at $20^\circ\text{C$. Take $20^\circ\text{C}$ as the reference temperature and the temperature coefficient of resistance of silver at $20^\circ\text{C}$ as $4.0 \times 10^{-3} \, \text{K}^{-1}$.}