UPSC Physics Optional PYQs (CSE & IFoS)PYQs

What is a Josephson junction ? Explain the phenomenon of tunneling of charge carriers across such a junction. Discuss DC and AC Josephson effects. Mention some applications of this device.

Using the collector characteristics of a bipolar junction transistor, show how you can use it as a switch with one ON and one OFF state. Plot and describe the operation of this circuit for a sinusoidal input.

What are the advantages of MOSFET over JFET ? Draw and explain the structure and working of a MOSFET which can function both in enhancement and depletion modes.

Employing NAND gates, design a half adder circuit which can add two bits A and B and provide a sum S and a carry C as its output.

Describe the essential parts of an oscillator circuit using a block diagram. Design a Colpitts oscillator set to a frequency of 1500\text{ Hz} and explain how your design incorporates the essential parts of the oscillator circuit.

Explain the reduced zone scheme of plotting the energy bands in solids. On the basis of E vs k curve distinguish between conductors, semiconductors and insulators.

What is nearly free electron approximation? On the basis of this approximation explain the formation of energy bands in solids.

Distinguish between Einstein and Debye models of specific heats of solids. Obtain an expression for the specific heat of a solid on the basis of Debye model. Discuss the results for low and high temperature ranges.

Distinguish between classical and quantum theory of paramagnetism. Explain the paramagnetism of free electrons on the basis of F.D. distribution.

What is Josephson tunnelling? Distinguish between a.c. and d.c. Josephson effects.

Identify the above op-amp circuit. Estimate the net output voltage V_0.

Draw a two stage RC coupled transistor amplifier. Plot the frequency response and indicate the lower and upper cut off frequencies and the bandwidth.

What is Meissner effect ? Explain the conclusions drawn from the Meissner effect.

A type-II superconducting material with superconducting transition temperature T_c is placed in a magnetic field. What is the material state (normal or superconducting or mixed) for (i) T < T_c ; \quad H > H_{c_2} (ii) T > T_c ; \quad H < H_{c_1} (iii) T < T_c ; \quad H_{c_1} < H < H_{c_2} (iv) T < T_c ; \quad H < H_{c_1} (v) T > T_c ; \quad H > H_{c_2} where H_{c_1} and H_{c_2} are the lower and upper critical fields for a type-II superconductor.

Which of the waves out of (i) X-rays, (ii) de-Broglie waves due to electrons or neutrons will be suitable for crystal diffraction ? Justify your answer in terms of energies of these waves for 0 \cdot 1 \text{ nm}.

Show that the reciprocal lattice of a hexagonal lattice is a hexagonal lattice with a rotation of axes.

What do you understand by early effect in bipolar junction transistors ? What are its consequences ? Discuss briefly the advantage of using the BJT in the common collector configuration.

List the characteristics of an ideal OP-AMP. Write the expression for the output voltage in terms of input voltages and resistance values.

The resistance of silicon and germanium varies with temperature. But these are not used normally as thermistors. Why ? Name at least two widely used materials for making thermistors and give any five applications of thermistor.

Verify that the circuit shown below is an exclusive OR.