BE Construction Engineering Semester 1 (FE First Year) - 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. 

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.

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.

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. 

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. 

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.

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.