List of top Physics Questions asked in CBSE CLASS XII

Which of the following statements is true about mobility of charge carriers in a metal ?
Photons of frequency $\nu$ are incident on the surfaces of two metals A and B of threshold frequencies $\frac{\nu}{2}$ and $\frac{\nu}{3}$. The ratio of maximum kinetic energy of electrons emitted from metal A to that from metal B is :
Two coils are placed closed to each other. The mutual inductance of the pair of coils depends upon the :
The resistivity $\rho$ of a metal increases with rise in temperature because :
A galvanometer of resistance $G$ is converted into a voltmeter of range $(0 - V)$ by connecting a resistor of $250\ \Omega$ with it. If resistor of $250\ \Omega$ is replaced by another resistor of $900\ \Omega$, its range becomes $(0 - 3\text{ V})$. The resistance $G$ of the galvanometer is :
Assertion (A) : When a convex lens made of glass is immersed in water, its converging power increases.
Reason (R) : The focal length of a lens depends only on the radii of curvature of its two faces.
Two particles of masses $m_1$ and $m_2$ having charges $q_1$ and $q_2$ respectively are projected with the same velocity in a region of uniform magnetic field $\vec{B}$ pointing vertically upward. If they describe circular paths as shown in the figure, one may conclude that :
The kinetic energy of a charged particle is increased to four times of its initial value. The de Broglie wavelength associated with the particle will :
In a reversed-biased p-n junction diode, the applied voltage mostly drops across :
An ac voltage is given as $v = 14 \sin (314t)\text{ V}$. The average and the effective value of the voltage (in V) over a cycle are respectively :
Paschen series in spectrum of hydrogen atom lies in :
An ac voltage $V = 280 \sin(100\pi t)$ volt is connected across a series LCR circuit in which $R = 400 \Omega$, $L = 5/\pi \text{ H}$ and $C = 50/\pi \mu\text{F}$. Taking $\sqrt{2} = 1.4$, calculate power factor of the circuit.
An ac voltage $V = 280 \sin(100\pi t)$ volt is connected across a series LCR circuit in which $R = 400 \Omega$, $L = 5/\pi \text{ H}$ and $C = 50/\pi \mu\text{F}$. Taking $\sqrt{2} = 1.4$, calculate rms value of current that flows in the circuit.
State Lenz's law and explain that it follows the law of conservation of energy.
Radiation of wavelength $331\text{ nm}$ irradiates the following metals:
An ac voltage $V = 280 \sin(100\pi t)$ volt is connected across a series LCR circuit in which $R = 400 \Omega$, $L = 5/\pi \text{ H}$ and $C = 50/\pi \mu\text{F}$. Taking $\sqrt{2} = 1.4$, calculate impedance of the circuit.
The ratio of amplitude of electric field to the amplitude of the magnetic field associated with an electromagnetic wave propagating in glass ($n = 1.5$) is :
Write the dimensional formula for self-inductance. The current in a coil changes from 8.0 A to 2.0 A in 0.6 s. If an average emf induced in the coil is 50 V, calculate the self-inductance of the coil.
A light bulb and an open coil inductor are connected in series across an ac source of variable frequency. How will the glow of the bulb be affected when an iron bar is inserted inside the coil ? Justify your answer. Assume that other factors remain unchanged.
Two infinitely long straight wires having linear charge densities $-\lambda$ and $3\lambda$ are held vertically parallel to each other, distance r apart in free space. Find the nature and magnitude of the force/length exerted by one wire on the other.
A small hollow conducting sphere of radius $r_1$ is given a charge Q. It is surrounded by a concentric conducting spherical shell of inner radius $r_2$ and outer radius $r_3$, having charge $-3q$. If a point charge 2q were kept at the centre, find electric field at a point distant x from the centre for (1) $x > r_3$, and (2) $r_1 < x < r_2$.
A light bulb and an open coil inductor are connected in series across an ac source of variable frequency. How will the glow of the bulb be affected when the frequency of the source is decreased ? Justify your answer. Assume that other factors remain unchanged.
A small hollow conducting sphere of radius $r_1$ is given a charge Q. It is surrounded by a concentric conducting spherical shell of inner radius $r_2$ and outer radius $r_3$, having charge $-3q$. If a point charge 2q were kept at the centre, find the electric flux through a concentric spherical Gaussian surface of radius x for (1) $x < r_1$, and (2) $r_1 < x < r_2$.
Two point charges $-2\mu C$ and $5\mu C$ are placed at $(-30 \text{ cm}, 0)$ and $(30 \text{ cm}, 0)$ respectively in an external electric field $\vec{E} = \frac{A}{x^2} \hat{i}$, where $A = 9 \times 10^5 \text{ Nm}^2\text{C}^{-1}$. Find the electrostatic potential energy of this configuration.
A small hollow conducting sphere of radius $r_1$ is given a charge Q. It is surrounded by a concentric conducting spherical shell of inner radius $r_2$ and outer radius $r_3$, having charge $-3q$. If a point charge 2q were kept at the centre, find surface charge density on the inner surface of (1) sphere, and (2) shell.