Engineering Answers

1.

Question 1

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Consider a step pn junction made of silicon. The p- and n-sides are doped such that E_C - E_F = 0.21 eV on the n-side and E_F - E_V ​=0.18eV on the p-side. The pn junction is under zero bias and kept at T=300K.

Find the doping density in the n-side in unit of cm^-3

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Answers within 5% error will be considered correct.

2.

Question 2

Find the doping density in the p-side in unit of cm^-3

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Answers within 5% error will be considered correct.

3.

Question 3

Find the built-in potential in unit of V

Answers within 5% error will be considered correct.

Tank A which is at a pressure of 1200 kPa, supplies 400 L/min of medium fuel oil to operate a hydraulic press via a 1” schedule 40 steel pipe. The medium fuel oil then exits the hydraulic press and returns to the pressurized tank A via a pump through 2” schedule 40 steel pipes. The pump is rated at 10 hp and has an efficiency of 90%. If the following data are known:

·        Energy loss from tank A to the hydraulic press inlet is 5.4 Nm/N.

·        Energy loss from hydraulic press outlet to the pump inlet is 0.8 Nm/N.

·        Energy loss from outlet of pump to tank A inlet is 1.8 Nm/N.

Ignoring all other losses, compute the following:

1.        Pressure at the hydraulic press inlet.

2.        Pressure at the pump outlet.

3.        Pressure at the pump inlet.

4.        Pressure at the hydraulic press outlet.

5.        Power removed from the fluid by the hydraulic press

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A 1.5m long column has a circular cross section of 5 cm in diameter. One of the ends of the columns is fixed in direction and position and the other end is free. Given that the factor is safety is 3. Calculate the safe load through the use of

(i) Rankine's formula, take that the yield stress as 560 N/mm² and α = 1/600 for pinned ends

A rigid flange coupling is used to connect a 45KW 1440rpm electric motor to a centrifugal pump. The starting torque of the motor is 225% of the rated torque. There are 8 bolts and their pitch circle diameter is 150mm . The bolts are made of steel 45C8 (sigma yt 380N/mm2 ) the factor of safety is 2.5 . Determine the diameter of the bolts. Assume (sigma sy 0.577 sigma yt) . Assume that the bolts are finger tight is reamed and ground holes.

Assume a 4-bit shift register using D flip flop which will take one clock cycle for loading the data and 3 clock cycles for getting the output, Identify the type of shift register and describe its operation with a diagram

Design a mealy machine whose output is 1 only when input 1101 is detected otherwise output is 0 with overlapping allowed and not allowed conditions.

Design a synchronous counter by using T-flip-flop which can counter the sequence 0, 1,2,4,5,0….and rest states move to 0.

Design a Mod -5 asynchronous up counter using +ve edge triggering D flip flop