Electrical Engineering Answers

Explain schematically different mechanisms associated with the growth of thin films

1.      Consider a square plate of 0.5 m x 0.5 m in a room at 30 C. One side of the plate is kept at a uniform temperature of 74 C while the other side is insulated. Determine the rate of heat transfer from the plate by free convection under the following three situations: (i) The plate is kept vertical (ii) The plate is kept horizontal with hot surface facing up (iii) The plate is kept horizontal with hot surface facing down.

A cylindrical pill-like cluster of radius r nucleates on a dislocation that emerges from the substrate. The free-energy change per unit thickness is given by

∆G =πr^2∆G, + 2myr + A - B Inr, where A - B Inr represents the dislocation energy within the cluster. 0).

(a) Sketch ∆G vs r (note at r= 0, G

(b) Determine the value of r*.

(c) Show that when ∆G, B/ry >+, ∆G monotonically decreases with r,

but when ∆G, B/ay² < there is a turnaround in the curve. (The latter case corresponds to a metastable state and associated energy barrier.)

What is meant by lattice mis-fit? How this parameter is important for the deposition of epitaxy layer of a desired semiconductor thin film? Answer with suitable example.

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A cylindrical pill-like cluster of radius r nucleates on a dislocation that emerges from the substrate. The free-energy change per unit thickness is given by

DG = pr2Gv + 2pyr + A - B ln r,

where A — B In r represents the dislocation energy within the cluster.

(a) Sketch DG vs r (note at r = 0, DG = µ

(b) Determine the value of r*.

(c) Show that when AGvJB/7iy2 > i, AG monotonically decreases with r, but when AGvB/7ry2 < i, there is a turnaround in the curve. (The latter case corresponds to a metastable state and associated energy barrier.)

The step-down chopper has the following datar Ra=0:35 E-480V, and Eb=20 V. Old=190A and chopper frequency=300 Hz Assuming the load current waveform to be linear, calculate the inductance L. which would limit the maximum load current ripple to 14% of the average load current

Full converter is connected to a 120-V, 60-Hz supply. The load current la is continuous and its ripple content is negligible. If the trigger angle is a n/3, calculate Video, Vrms, THE, DF, and PF.

A one sided p

+

-n junction at 300K is doped with NA = 1019cm-3

. Design the

junction so that depletion capacitance is 0.85 pfd at Vr = 4V.

A salient pole synchronous generator has the following per unit parameters;xd=1.2,xq=0.8 ra=00.025. compute the excitation voltage Ef on a per unit basis,when the generator is delivering rated kva at rated voltage and at power factor of 0.8 lagging and 0.8 leading

An iron ring has a mean diameter of 15 cm, a cross-section of 20 cm ^ 2 and a radial air gap of 0.5 mm cut on it. The ring is uniformly wound with 1500 turns of insulated wire and a magnetizing current of 1A produces a flax of 1 mWb in the air gap. Calculate: (i) the reluctance of the magnetic circuit and fii the relative normoabilit of t [5]