List of top Physics Questions asked in CBSE CLASS XII

A signal, as shown in the figure, is applied to a p-n junction diode. Identify the output across the resistance \( R_L \):
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:
In a full-wave rectifier, the current in each of the diodes flows for:
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 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:
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:
State any two properties of a nucleus.
(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?
"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.
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.
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,
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 $\alpha = \left( \frac{ne^2}{m} \right) \tau$.}
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
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
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.
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.}
Assertion (A): Plane and convex mirrors cannot produce real images under any circumstance.
Reason (R): A virtual image cannot serve as an object to produce a real image.
Assertion (A): Two long parallel wires, freely suspended and connected in series to a battery, move apart.
Reason (R):Two wires carrying current in opposite directions repel each other.
Assertion (A): The mutual inductance between two coils is maximum when the coils are wound on each other.
Reason (R): The flux linkage between two coils is maximum when they are wound on each other.
Assertion (A): In photoelectric effect, the kinetic energy of the emitted photoelectrons increases with increase in the intensity of the incident light.
Reason (R): Photoelectric current depends on the wavelength of the incident light.
The waves associated with a moving electron and a moving proton have the same wavelength $\lambda$. It implies that they have the same:
Ge is doped with As. Due to doping:}
The transition of electron that gives rise to the formation of the second spectral line of the Balmer series in the spectrum of hydrogen atom corresponds to:
In the four regions, I, II, III, and IV, the electric fields are described as: Region I: $E_x = E_0 \sin(kz - \omega t)$
Region II: $E_x = E_0$
Region III: $E_x = E_0 \sin kz$
Region IV: $E_x = E_0 \cos kz$
The displacement current will exist in the region: