UPSC Physics Optional PYQs (CSE & IFoS)PYQs

How does build in potential appear across a p-n junction? Explain under what biasing conditions drift and diffusion currents, respectively, dominate.

Draw the block diagram of a superhetro dyne radio receiver and explain the function of local oscillator.

Explain why even-even nuclei are more stable than odd-odd nuclei.

State conservation laws obeyed by strong and weak interactions.

What is space quantisation? Discuss the Stern Gerlach experiment establishing the space quantisation.

What are the term symbols of 2 equivalent p electrons? Write down the term symbols in ascending order of energies.

Explain the orgin of anti-Stokes lines in Raman spectra.

Using Heisenberg Uncertainty principle, calculate the mass of meson being exchanged between nucleons inside the nucleus, taking the range of nuclear force as 1.7 F. Distinguish between pion and muon.

An electron is confined in a one dimensional box 1 Å width. Draw the energy level diagram upto three energy stats of also draw the corresponding normalized eigen function. Derive the expressions for eigen functions and eigen values used in the calculations. Show that eigen functions are othogonal.

Describe how Davisson-Germer electron diffraction experiment confirms the de Broglie hypothesis of matter wave.

Calculate the most probable speed v_p, the avenge speed \langle v \rangle and the root-mean-square speed \langle v^2 \rangle^{1/2} for hydrogen molecules at 273\text{ K}.

Write the expressions obtained from Einsteins’s and Debye’s theories for the specific heat of solids. What is the basic difference between the two theories? Calculate the heat required to raise the temperature of a solid of mass m from T_1 to T_2 in the low temperature region.

Hydrogen and oxygen suffer Joule - Thomson expansion at room temperature. Discuss the results with reasons.

State Nernst’s heat theorem. Taking the example of adiabatic demagnetisation show that no adiabatic process initiated at non-zero-temperature can lead to zero temperature.

Define thermodynamic temperature of a magnetic system. Discuss how cooling takes place due to adiabatic demagnetisation. Explain, why cooling due to adiabatic demagnetisation is important at low temperatures.

Write a short note on Brownian motion.

Write a short note on Concept of negative temperature.

Define entropy, Derive expressions for the entropy of a perfect gas in terms of (i) T and v (ii) T and p The symbols have their usual meanings.

An electric dipole is placed in an external electric field. Find the interaction energy between the electric dipole and the field. And hence find the force and the torque acting on the dipole.

Starting from Maxwell equations obtain differential equations for scalar and vector potentials. Choosing the required gauge obtain identical differential equations for scalar and vector potentials. Solve the equation for scalar potential in a dielectric medium having a source of charge density p.