PYQ Bank

Starting from an expression for the group velocity, arrive at an expression for the effective mass of an electron in a semiconductor. Explain the significance of sign of the effective mass.

What is Meissner effect ? Determine the magnetic susceptibility of a superconductor. Explain whether a superconductor exhibits perfect ferromagnetism, paramagnetism or diamagnetism.

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} The above circuit exhibits a MOSFET with a source resistor. It has V_T = 1\text{ V} and \mu_n C_{ox} (W/L) = 2\text{ mA/V}^2. Calculate the drain voltage. Also determine whether the transistor is in saturation or in the triode region.

Using OP-AMPs design an analog circuit to solve the following differential equation : \frac{d^2 v}{dt^2} + k_1 \frac{dv}{dt} + k_2 v = v_1(t) with \frac{dv_{(0)}}{dt} = 1\cdot 5\text{ V}; v_{(0)} = 2\cdot 0\text{ V}.

Explain the basic structure and operation of an n-channel FET. How FET acts as an amplifier ? Explain.

Explain the origin of energy band formation in solids. Show that in nearly free electron approximation, the energy band gap is 2|V_G|, where V_G is Fourier transform of periodic potential seen by the valence electrons.

Find an expression for lattice specific heat of solids, and its low and high temperature limits. What is Debye temperature?

How are the band structures of insulators and semiconductors similar ? How are they different ?

Using band theory of solids, explain whether the effective mass of an electron can be positive, negative as well as infinity. Explain the significance of negative mass.

Derive Bragg diffraction condition in vectorial form using incident and diffracted wave vectors and reciprocal lattice vector.

Describe the characteristic properties of a superconductor. Derive London equation for a superconductor and hence explain Meissner effect.

Simplify the logical expression \overline{(A+B)}B(A+\bar{C}) and draw the logical circuit to implement it.

Simplify the logical expression AB + \bar{A}\bar{B} + ABC using a Karnaugh map.

An electron beam of 4 Kev is diffracted through a Bragg angle of 16^\circ for the first maxima. If the energy is increased to 16 keV, find the corresponding Bragg angle for diffraction.

Distinguish between intrinsic and extrinsic semiconductors. Show that in a semiconductor, the product of concentrations of the two types of charge carriers is constant at a given temperature.

Draw the common-base amplifier circuit, using an n-p-n transistor and briefly discuss its working.

(i) What are intrinsic and extrinsic semiconductors ? Explain. (ii) How are n-type and p-type semiconductors obtained ?

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.

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.