BE Mechanical Engineering Semester 1 (FE First Year) - University of Mumbai Question Bank Solutions

Define the term drift current and mobility of a charge carriers. Calculate the current product in a germanium sample of area of cross section 1 cm² and thickness of 0.01 m, when a potential difference of 2V is applied cross it. Given :- the concentration of free electron in germanium is 2×10¹⁹ /m³  and mobilities of electrons and holes are 0.36 m² /volts sec and 0.17 m² /volts sec respectively.

What do you mean by group and phase velocity? Show that the de-Broglie group velocity associated with the wave packet is equal to the velocity of the particle.

The mobility of holes is 0.025m² /V-sec. what would be the resistivity of n- type Si if the Hall coefficient of the sample is 2.25× 10^-5m³/C. 

Define drift current, diffusion current and P-N junction. The electrical conductivity of a pure silicon at room temperature is 4×10^-4 mho/m . if the mobility of electron is 0.14m² /V-S and that of hole is 0.04m² /V-S. calculate the intrinsic
carrier density.

What is the wavelength of a beam of neutron having:
⦁ An energy of 0.025 eV?
⦁ An electron and photon each have wavelength of 2A°. what are their momentum and energy ? m_n = 1.676×10^-27 kg, h = 6.625×10^-34 J-sec. 

Calculate the frequency and wavelength of photon whose energy is 75eV.

Mobility of electron and hole in a sample of Ge at room temperature are 0.36 m² /V-sec and 0.17m² /V-sec respectively. If electron and holes densities are equal and it is 2.5 ×10¹³ /cm³ , calculate its conductivity.

State the piezoelectric effect. With neat circuit diagram explain the principle and working of piezoelectric oscillator .

Calculate electron & hole concentration in intrinsic Si at room temperature if
its electrical conductivity is 4x10-4 mho/m.Given that mobility of electron=
0.14m2/V-sec and  mobility of holes=0.04m2/V-sec.

Show that for intrinsic semiconductors of the Fermi level lies midway between the conduction band and the valence band .With the help of diagram explain effect of impurity concentration on Fermi level of N type semiconductor.

For an electron passing through potential difference V, show that its
wavelength is; 

λ = 12.26/√V A°.

Write Fermi Dirac distribution function. With the help of diagram. Explain the variation of Fermi level with temperature in n-type semiconductor.

Write the Fermi Dirac distribution function and terms in it. What is the probability of an electron being thermally excited to the conduction band in Si at 30 ℃. The band gap energy is 1.12 eV. 

Differentiate between Type-1 & Type- II Superconductors.

Discuss formation of copper pairs and energy gap in superconductor on the basis of BCS theory.

 Explain analysis of crystal structure using Bragg’s X ray spectrometer

Why X-rays are used to study the crystal structure?

‘Crystal acts as three dimensional grating for X-rays’, explain.

State properties of matter waves.

Derive Bragg's condition for X-ray diffraction. Monochromatic X rays are
incident on a crystal. If the first order rejection is observed at an angle of 3.4•, at
what angle would second order reflection expected.