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

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.

Derive an expression for Hall voltage and Hall coefficient with neat labelled diagram.

What is the probability of an electron being thermally excited to conduction
band in Si at 27cC.The band gap energy is 1.12 eV.

Calculate conductivity of a germanium sample if a donar impurity atoms are added to the extent to one part in 10⁶  germanium atoms at room temperature.
Assume that only one electron of each atom takes part in conduction process.

Given:- Avogadro’s number = 6.023 × 10²³ atom/gm-mol . 
Atomic weight of Ge = 72.6

Mobility of electrons = 3800` (cm^2) / ( "volts") `sec

Density of Ge = 5.32 gm/ cm³

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

What is Maglev? How it can have very high speed?

Define the critical temperature. Slow that in the superconducting state the material is perfectly diamagnetic. 

What is working principle of SQUID ? Explain how it is used to detect the magnetic field?

What is the working principle of maglev? Explain how it can acquire high speed?

Explain Meissner Effect with the help of diagram.

Differentiate between Type-1 & Type- II Superconductors.

What is reverberation time? Discuss sabine formula. 

State any five factors affecting the acoustics of the building and give the remedies for each. 

Explain the factors on which reverberation time depends .

A classroom has dimension 10×8×6m³. the reverberation time is 3 sec. calculate the total absorption of surface and average absorption. 

A conference room has a total volume of 2000 m3.The magnitude of total
absorption with in the conference room is100 Sabin.Calculate thereverberation time.

Discuss in details any three factors affecting acoustics of a hall with their
remedies.

State ‘magnetostriction effect’. Mention any two application of ultrasonic waves

An ultrasonic pulse of 0.09M Hz sends down towards the sea-bed which returns after 0.55 seconds. The velocity of ultrasonic waves in sea water is 1800 m/sec . calculate the depth of sea and wavelength of ultrasonic pulse.