List of top Questions asked in UP Board XII

Explain the difference between conductors and semiconductors on the basis of energy bands in solids.

A rectangular glass slab ABCD of refractive index \(n_1\) is placed in a liquid of refractive index \(n_2\) (\(n_1 > n_2\)). A ray of light is incident at the surface AB of the slab as shown in the figure. Find out the maximum value of angle \(\alpha\), so that the ray comes out only from the other surface CD.
What is the phenomenon of radioactivity? How many types are there of radioactive decay?
What will be the effect on the drift velocity of electrons, when the current in a copper wire is passed in a wire, twice of its radius (the same current being maintained)?
Work function of a metal surface is 3.2 eV. Find out the kinetic energy of the emitted photoelectrons in Joule, when a photon of 4.0 eV energy is incident on its surface.
What is an equipotential surface?
What is the difference between paramagnetic and diamagnetic substances?
Define and write the formula of mobility.
What are the uses of microwaves?
Equivalent resistance \( R \) is obtained when \( n \) wires having the same length and same thickness of the same material are joined in parallel. The equivalent resistance on joining them in series will be:
What is meant by the optical center of a lens?
What are the charge carriers in p-type of semiconductors?
A coil of one loop is formed by a wire of length \( L \), and thereafter a coil of 3 loops is formed by the same wire. If the current remains the same in both cases, then the ratio of the magnetic fields at the centre will be:
In which of the following spherical mirrors is the magnification of the image always less than 1?
Coulomb's repulsive force of \( F \) newton acts between two point charges of \( +3\,\mu C \) and \( +8\,\mu C \). If \( -5\,\mu C \) charge is given to both of them, then the force and its nature between them will be:
In the given nuclear reaction, particle W is: \[ {}_{2}^{4}\text{He} + {}_{Z}^{A}X \ \rightarrow\ {}_{Z+2}^{A+3}Y + W \]
If the accelerating potential of a moving charged particle of \( \lambda \) de Broglie wavelength is increased by four times, then the de Broglie wavelength will be:
When an impurity is doped in a pure semiconductor, the conductivity of the semiconductor
How can p-type and n-type crystal from pure semiconductor be formed? Find the maximum wavelength of electromagnetic radiation which can create a hole-electron pair in germanium of a band-gap 0.65 eV.
OR
How is the conductivity of a metal and semiconductor changed with raising temperature? Calculate the conductivity of an n-type semiconductor from the following data: Density of conduction electrons = 8×1013 /cm3, Density of holes = 5×1012 /cm3, Mobility of conduction electrons = 2.3×104 cm2/V·s, Mobility of holes = 100 cm2/V·s.
Show the position of focus (f) in ray diagram for convex mirror. At what distance from a convex mirror of focal length 2.0 m should a boy stand so that his image has a height equal to half the original height?
OR
What is wavefront? Explain the refraction of waves with the help of Huygens' principle.

Option 1: With the help of the given figure, prove that the magnetic field produced at point P is \(B=\dfrac{\mu_0 i}{2d}\left[1+\dfrac{2}{\pi}\right]\). (The wire is hairpin-shaped: a semicircular arc joined to two long straight parallel segments carrying current \(i\); P is at the centre of the arc and the straight segments are a distance \(d\) apart.)
OR
Option 2: What is a radial magnetic field? Explain the working of a moving coil galvanometer with a suitable diagram. How can a galvanometer be converted into an ammeter and a voltmeter?
Energy of the \(n^{th}\) state of a hydrogen atom is \(E_n=-\dfrac{13.6}{n^2}\ \text{eV}\). A hydrogen sample is prepared in a particular excited state A. Photons of energy \(2.55\ \text{eV}\) get absorbed by the sample to take some electrons to a particular further excited state B. Find the quantum numbers of states A and B.

Option 1: What is Gauss's law? The figure shows a cylinder placed in an electric field \(\vec{E}=100\,\hat{i}\ \text{N/C}\). \(\vec{E}\) is positive when \(x>0\) and negative when \(x<0\). Length of the cylinder is \(30\ \text{cm}\) and radius of each plane surface is \(3.5\ \text{cm}\); its centre is at O. Find the electric fluxes \(\phi_1,\ \phi_2\) and \(\phi_3\) linked with each plane and the curved surface respectively. What will be the net charge inside the cylinder?
OR
Option 2: Obtain the formula for the capacitance of a parallel plate capacitor when a dielectric medium is partially filled in between its plates.
Write the characteristics of nuclear force. How is it different from gravitational and electric (electrostatic) forces?

In the figure, the plot of stopping potential versus frequency of light used in an experiment of the photoelectric effect is shown. Find the ratio \( h/e \) and the work function.
(From the graph: the line meets the frequency axis at \( \nu_0 = 1\times10^{15}\ \text{Hz} \), and the stopping potential is \( V = 1.656\ \text{V} \) at \( \nu = 5\times10^{15}\ \text{Hz} \).)