ELECTRONICS ENGINEERING DIFFICULT QUESTION

1. How many SCRs are required in a series string to withstand a DC voltage of 3500 volts in steady state, if the SCRS have steady state voltage rating of 1000V and steady state derating factor of 30%? Assuming a difference in leakage current of SCR’s to be 10 mA, calculate the value of voltage sharing resistances to be used.

ANSWER: 5

2. It was a term coined in 1971 by circuit theorist Leon Chua as a missing non-linear passive two-terminal electrical component relating electric charge and magnetic flux linkage. It is basically a fourth class of electrical circuit, joining the resistor, the capacitor, and the inductor, that exhibit their unique properties primarily at the nanoscale.

ANSWER: MEMRISTOR

3. This type of memory is basically an arrangement of shift registers. It is used in applications where two systems communicate at different rates.

ANSWER: FIFO or FIRST IN – FIRST OUT

4. It is the fastest switching speeds compared to any logic IC’s. It consumes more power than TTL and eliminates the turn-off delay. Input logic levels are limited to a narrow voltage range to reduce the large power dissipation resulting from the active mode. Determine the type of current mode logic family.

ANSWER: ECL or Emitter Coupled Logic

5. Find the average drift velocity in a silicon semiconductor doped with phosphorus. Assume doping density of 1 per million, a cross-sectional area of 10-4 m2, a current of 4 A, and the concentration of silicon atoms in a silicon crystal is nsi = 4.96 x 1028 atoms/m3.

ANSWER: 5 m/s

6. Give the common name for what was later standardized as the IEEE 1149.1 or the Standard Test Access Port and Boundary-Scan Architecture. It was initially devised for testing printed circuit boards using boundary scan and is widely used for this application.

ANSWER: JTAG OT JOINT TEST ACTION GROUP

7. What net flux crosses the closed surface S which contains a charge distribution in the form of a plane disk of radius 4m

with a density Ρs=(sin∅ )2

2r ( Cm2 )ANSWER: 2π C

8. Find the output voltage

ANSWER: 442 mV

9. In the circuit shown below, the outputs Y1 and Y2 for the given initial condition Y1 = Y2 = 1 and after four input pulses will be

ANSWER: Y1=1, Y2=1

10. A three-phase half-controlled thyristor converter has an highly inductive load of 10 ohms, and a supply of 240V at 50Hz. Determine the value of the power factor for firing angle delay of a = 30O.

ANSWER: 0.585

11. Determine the frequency of oscillation of a phase shift oscillator with R1 = R2 = 15 kΩ and C1 = C2 = C3 = 0.001 µF.

ANSWER: 4.33 kHz

12. It is the production of an electromotive force (emf) and consequently an electric current in a loop of material consisting of at least two dissimilar conductors when two junctions are maintained at different temperatures.

ANSWER: SEEBECK EFFECT

13. Find E at P(1, 1, 1) caused by four identical 3 nC point charges located at P1(1, 1, 0), P2(- 1, 1, 0), P3(- 1, - 1, 0) P4(1, - 1, 0).

ANSWER: 6.82ax + 6.82ay + 32.89az V/m

14. A three bit pseudo random number generator is shown. Initially the value of output Y = Y2 Y1 Y0 is set to 111. The value of output Y after three clock cycles is

ANSWER: 100