BE Chemical Engineering छमाही १ (इंजीनियरिंग) - University of Mumbai Important Questions

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

λ = 12.26/√V A°.

Show that group velocity of matter waves associated with a particle is equal to
the particle velocity(V_group=V_particle)

Explain the principle, construction and working of Light Emitting Diode.

Draw the I-V characteristics of a photo -diode. What is meant by dark current?

Define super conductivity and critical temperature. Plot the variation of resistance versus temperature in case of superconducting state of the material. 

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.

State application of Hall effect. In a Hall effect experiment a potential difference of 4.5 μV is developed across a foil of zinc of thickness 0.02mm when a current of 1.5 A is carrying in a direction perpendicular to applied magnetic field of 2 tesla. Calculate :-

• Hall coefficient for zinc.

•  Concentration of electron.

How does the position of fermi energy level changes with increasing doping concentration in p-type semi-conductor ? sketch diagram.

Find the minimum energy of neutron confined to a nucleus of size of the order of 10^-14m. Given mass of neutron = 1.675×10^-27kg 

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. 

Explain the concept of fermi level. Prove that the Fermi level exactly at the centre of the Forbidden energy gap in intrinsic semiconductor.

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.

Distinguish between Type I and Type II superconductor.

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

Find the depth of sea water from a ship on the sea surface it the time interval of two seconds is required to receive the signal back. Given that: temperature of sea water is 20℃, salinity of sea water is 10gm/lit. 

In a solid the energy level is lying 0.012 eV below Fermi level. What is the probability of this level not being occupied by an electron 27℃?

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. 

With energy band diagram , explain the variation of fermi energy level with impurity concentration in extrinsic semiconductor. 

Show that fermi energy level in intrinsic semiconductor is at the Centre of forbidden energy gap. 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.

With energy band diagram ,explain the variation of fermi energy level with temperature in extrinsic semiconductor .