UPSC Physics Optional PYQs (CSE & IFoS)PYQs

Explain the term critical magnetic field in a superconductor. How does the critical magnetic field vary with temperature in Type-I and Type-II superconductors ? What is Meissner effect ?

With a suitable circuit diagram and theory explain the use of OP-Amps as

(i) Adder, and

(ii) Integrator.

What are called intrinsic and extrinsic semiconductors ?

Construct the following function with logic gates : Y = (A + B) (C + D + E) (F + G + H + I) (JKL)

Show that any arbitrary rotation axis is not permitted in a crystal lattice.

An electric field of 100\ \mathrm{V/m} is applied to a sample of n-type semiconductor whose Hall coefficient is -0.0125\ \mathrm{m^3/coulomb}. Determine the current density in the sample assuming \mu_x = 0.36\ \mathrm{m^2\,V^{-1}\,s^{-1}}.

For the logical equation given below, form the truth table and draw the corresponding logic circuit using different gates : Y = A \cdot B + \overline{A \cdot B}

Show that the NAND gate is a universal gate.

Explain with the help of a neat diagram the structure of a n-channel FET and its IV characteristics. In what way is an FET different from a BJT ?

A silicon diode operates at a forward bias voltage of 0\cdot 4\text{ V}. Calculate the factor by which the current will be multiplied when the temperature is increased from 25^\circ\text{C} to 150^\circ\text{C} (\eta for \text{Si} = 2).

In a cubic unit cell, find the angle between normals to the plane (111) and (121).

Explain the working of SEM and TEM and highlight the major differences in principles. Draw neat schematic diagrams.

What is ac Josephson effect ? Derive an expression for the current flowing through the junction formed by two superconducting films separated by an insulator.

What is the reciprocal lattice and why is it named so? Derive the relationships for the primitive translation vectors of the reciprocal lattice in terms of those of the direct lattice.

X-ray of wavelength 1\cdot 4\text{ \AA} is found to be Bragg reflected from (111) plane of an fcc structure. If the lattice parameter of the crystal is 5\text{ \AA}, find the angle at which the X-ray beam is incident on the (111) plane of the crystal.

How does the energy gap in superconductors differ from the energy gap in insulator? How does it vary with temperature for superconductors?

Lead in the superconducting state has critical temperature of 6.2\ \mathrm{K} at zero magnetic field and a critical field of 0.064\ \mathrm{MA\,m^{-1}} at 0\ \mathrm{K}. Determine the critical field at 4\ \mathrm{K}.

The velocity of sound in f.c.c. gold and f.c.c. copper is 2100\,\mathrm{m/s} and 3800\,\mathrm{m/s} respectively. If the Debye temperature of copper is 348\,\mathrm{K}, then determine the Debye temperature of gold. Take the densities of gold and copper as 1.93 \times 10^{4}\,\mathrm{kg/m^3} and 0.89 \times 10^{4}\,\mathrm{kg/m^3} respectively.

Can you comment from the above question whether you can use it to scan surface by microscopy?

A crystal plane is shown in the above figure. Find its Miller indices and interplanar spacing.