Tribhuvan University
Institute of Science and Technology
TU Exam Year: 2078
Candidates are required to give their answers in their own words as far as practicable.
SECTION A
Attempt all questions.
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1.
Discuss electrical conductivity of semiconductors. Derive expression for conductivity in terms of impurity ionization energy. Give a plot to discuss 'Theoretical temperature dependence of the electrical conductivity of an impurity semiconductor'.
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2.
Describe processes involved in the fabrication of integrated circuits include epitaxial growth, oxidation, oxide removal and pattern definition, doping (impurities in the Si), and interconnection of components.
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3.
Find expression for force on a current-carrying wire in a magnetic field to find the force experienced by a single charge.
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4.
Give spectrum of Hydrogen atom and discuss its lines.
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5.
Give a brief account of Kronig-Penny model.
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6.
Describe the term 'space quantization'.
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7.
A given spring stretches \( 10^{-4} \) m when a force of 20N pulls on it. A 2-kg block attached to it on a frictionless surface is pulled to the right 0.2 m and released.
(a) What is frequency of oscillation of the block?
(b) What are the velocity and acceleration when \( x = 0.12 \) m, on the block's first passing this point? -
8.
A proton is moving with a velocity \( \vec{v} = (3 \times 10^5 \hat{i} + 7 \times 10^5 \hat{k}) \) m/sec in a region where there is a magnetic field \( \vec{B} = 0.4 \hat{j} \) T. Find the force experienced by the proton.
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9.
In neutron spectroscopy a beam of mono-energetic neutrons is obtained by reflecting reactor neutrons from a beryllium crystal. If the separation between the atomic planes of the beryllium crystal is \( 0.732\ \text{\AA} \), what is the angle between the incident neutron beam and the atomic planes that will yield a monochromatic beam of neutrons of wavelength \( 0.1\ \text{\AA} \)?
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10.
(a) How many atomic states are there in hydrogen with \( n = 3 \)?
(b) How are they distributed among the sub shells? Label each state with the appropriate set of quantum numbers \( n, \ell, m_\ell, m_s \).
(c) Show that the number of states in a shell, that is, states having the same \( n \), is given by \( 2n^2 \). (Hint: \( 1 + 2 + 3 + \dots + n = \frac{n(n+1)}{2} \)) -
11.
The density of aluminum is 2.70 g/cm³ and its molecular weight is 26.98 g/mole.
(a) Calculate the Fermi energy.
(b) If the experimental value of \( E_F \) is 12 eV, what is the electron effective mass in aluminum? [Aluminum is trivalent]. -
12.
Analyze the circuit shown in the figure below. Determine the logic function performed by the circuit by making and justifying the appropriate truth table.