UPSC Physics Optional PYQs (CSE & IFoS)PYQs

What is Meissner effect? Show that the Maxwell's equation is in contradiction to the Meissner effect. What are the inferences from this contradiction?

An n-p-n transistor with \alpha = 0\cdot 98 is operated in the CB configuration. If the emitter current is 3\text{ mA} and the reverse saturation current is I_{CO} = 10\text{ }\mu\text{A}, what are the base current and the collector current?

Why NAND and NOR gates are called universal gates? Give the logic diagram, Boolean equation and the truth table of a X–OR gate.

State the basic conditions for oscillations in a feedback amplifier. What are the primary requirements to obtain steady oscillations at a fixed frequency?

Explain the drawbacks of Einstein's theory of specific heat and how it was overcome by Debye.

Explain why Type-II superconductor is better than Type-I superconductor in the application of superconductor magnets.

Why is the Field Effect Transistor (FET) called Unipolar Transistor? Discuss how it is superior than Bipolar Junction Transistor.

(i) Prove the following using De Morgan's theorems : A \cdot B + C \cdot D = \overline{\overline{A \cdot B} \cdot \overline{C \cdot D}} (ii) Simplify the following expression : Y = A \cdot B \cdot \bar{C} \cdot D + \bar{A} \cdot B \cdot \bar{C} \cdot \bar{D} + B \cdot \bar{C} \cdot D

Considering atoms hard, uniform spheres, find the number of atoms per unit cell and packing fraction for simple cubic, bcc and fcc structures.

(i) Diamond and silicon have similar band structure. Why is diamond an insulator while silicon a semiconductor? (ii) An insulator has an optical absorption which occurs for all wavelengths lesser than 1400\text{ \AA}. Find the width of the forbidden energy band for the insulator.

The wavelength of a prominent X-ray line from a copper target is 0.1512\,\mathrm{nm}. The radiation, when diffracted with (111) plane of a crystal with fcc structure, corresponded to a Bragg angle of 20.2^\circ. If the density of the crystal is 2698\,\mathrm{kg/m^3} and atomic weight is 26.98\,\mathrm{kg/kmol}, calculate the Avogadro number.

Show that for an n-type semiconductor, the Fermi level lies midway between the donor states and the conduction band edge at low temperature (assuming E_v=0).

Compare the dependence of resistance on temperature of a superconductor with that of a normal conductor. Describe briefly the formation of Cooper pairs.

(i) Distinguish between d.c. Josephson effect and a.c. Josephson effect. Show that Josephson effect exhibits the quantum interference phenomenon on macroscopic scale. (ii) The critical magnetic field of superconducting niobium is 1 \times 10^5\text{ A/m} at 8\text{ K} and 2 \times 10^5\text{ A/m} at 0\text{ K}. Calculate the critical transition temperature (T_c) of niobium.

Describe briefly the functions of the basic segments of a microprocessor. Draw a block diagram of the registers in the 8085 microprocessor.

An X-ray beam of wavelength \lambda_1 undergoes a first order Bragg reflection at a Bragg angle of 30^\circ. X-ray of wavelength 97\,\mathrm{nm} undergoes 3rd order reflection at a Bragg angle of 60^\circ. Consider that the two beams are reflected from the same set of planes. Find the value of \lambda_1.

A solid contains a dilute concentration of \mathrm{Nd}^{3+} ions, each of which possess three 4f electrons. Assuming that there are 10^{25}\ \mathrm{m}^{-3} of these ions, calculate the magnetic susceptibility of the sample at 1\,\mathrm{K}.

Explain the high temperature superconductivity. What are different properties of high temperature superconductors ?

An n-p-n transistor with \beta = 49 is used in common-emitter amplifier mode with V_{cc} = 10\ \mathrm{V} and R_L = 2\mathrm{k}\Omega. If a 100\mathrm{k}\Omega resistor is connected between the collector and the base of the transistor, calculate the quiescent collector current. Assume V_{BE} = 0.

Draw the circuit diagram of a transistor operating in the common-base configuration and sketch its input and output characteristics. Indicate the active, cut-off and saturation regions.