# ISRO Entrance Exam - Electronics and Communication Engineering Questions

## ISRO Entrance Exam - Electronics and Communication Engineering Questions

1. Which losses are present in an induction motor for no load test?

A. Core, Friction and Windage losses

B. Only very small Cu losses

C. Copper, Windage and Friction Losses

D. Core, Iron and Cu losses

2. A generator with maximum prohibitive incremental transmission loss for effective economic operation will operate at:

A. Maximum negative incremental cost of production

B. Minimum positive incremental cost of production

C. Maximum positive incremental cost of production

D. Minimum negative incremental cost of production

3. A cascade type system of 3 linear time invariant parameters is causal and unstable. The conclusion that we draw out of this is:

A. Every system in the cascade is unstable and causal individually

B. At least one of the systems is unstable and at least one of the systems is causal

C. All systems are unstable and at least one system is causal

D. Majorities are unstable, minorities are causal

4. EHV transmission line’s insulation strength is actually administered by?

A. Corona

B. Harmonics

C. Switching over voltages

D. Load Power Factor

5. HVDC (High voltage Direct Current) transmission finds its use mainly for:

A. Minimization of harmonics at converter stations

B. Elimination of reactive power requirement

C. Interconnecting 2 systems which have exactly the same nominal frequency inbuilt

D. Manage bulk power transmission over long distances

6. Which of the following is true for a linear electromagnetic circuit?

A. Field energy is zero

B. Co energy is zero

C. Field energy and Co energy are equal

D. Field energy is less than co energy

7. Following information is given on a hydraulic turbine: It has a rated speed of 250 rpm and is connected to a synchronous generator. So as to produce a power measuring 50 Hz what are the number of poles required in the generator?

A. 24

B. 16

C. 12

D. 6

8. A 50 Hz, 500 MVA, 22Kv , 4 pole turbo generator delivers power at .8 power factor. Suddenly during the operation a fault occurs which reduces the output of electric power by 40%. Neglecting the losses and assuming a constant power input at the shaft. What will be the accelerating torque in the generator at time of the fault?

A. 1.528

B. 0.848

C. 1.018

D. .5017

9. For a fixed value of complex power flow in a dedicated line of transmission real power loss is proportional to

A. 1/V

B. 1/V2

C. V2

D. V

10. Consider the following 4 plants:

i. Nuclear

ii. Pump Storage

iii. Run of river

iv. Diesel

Which of the following are base load power plants?

A. I and II

B. I and II

C. I, III and IV

D. I, II and III

11. A boy walks along the diagonal of the field instead of walking along the adjacent sides of that rectangular shaped field and in the process saves a distance which is equivalent to half of the longer side. Find the ratio of shorter side to longer side:

A. 1:2

B. 3:4

C. 2:3

D. 1:4

12. In two samples, the proportion of milk and water is 5:2 and 7:5. A mixture is made which contains equal concentration of both the sample, proportion of milk and water in this mixture is?

A. 7:12

B. 12:7

C. 59:109

D. 109:59

13. An express train is moving at the speed of 80 km/hr and it overtakes a goods train whose length is two times the express train and it is moving in the same direction with a speed of 40 km/hr. Time taken to overtake that train is 54 seconds. What is the time taken by the express train to cross a station which is 400m long?

A. 27 seconds

B. 54 seconds

C. 18 seconds

D. None

14. A child was asked to add first few natural numbers till he desires. When he stopped the sum was 575. It was discovered that the child had missed one number in the sequence of addition. What was the number that he missed?

A. Less than 10

B. 10

C. 15

D. More than 15

15. There is a colony of bacteria in a container which grows by splitting into 8th next generation bacteria. However due to some environmental conditions only 50% of a single generation bacteria can split in this fashion. A flock of first generation bacteria was operated upon and hence it was found out that the number of seventh generation bacteria was 4096 million. Determine the size of 1st generation population of bacteria which was initially put inside the container

A. 2 million

B. 1 million

C. 4 million

D. 8 million

16. 5 fully skilled painters can paint a wall in 20 days, 8 partially skilled painters can paint a wall in 25 days, 10 unskilled painters take 30 days to paint the same wall. If a team is assembled which contains 2 skilled, 5 unskilled and 6 partially skilled workers how much time will it take for the team to build the wall?

A. 15 DAYS

B. 16 DAYS

C. 18 DAYS

D. 20 DAYS

17. Given the arrangement: 2,2,3,3,3,4,4,4 How many 4 digit numbers can you form out of these which are greater than 3000?

A. 50

B. 51

C. 54

D. 52

18. Harry, George, Indiana and Sarah are sibling. All of them were born on December 1. The age gap between any two successive siblings is at most 2 years. Here are some facts:

A. Harry’s age + George’s age > Indiana’s age a+ Sarah’s age

B. George and Sarah have 1 year gap. George is not the oldest and Sarah is not the youngest.

C. None of them are twins

Arrange the following in descending order of age

A. H S I G

B. I H S G

C. I G S H

D. S G H I

19. A Y-connected 3 phase 500 MW generator has a voltage rating of 21.5 KV at .85 power factor. What will be the line current operating at full load?

A. 27.45 KA

B. 23.35 KA

C. 15.79 KA

D. 13.43 KA

20. If in a certain code 137 + 276 = 435, what is the value of 731 + 672?

A. 513

B. 623

C. 637

D. 534

21. A rotating electrical machine contains self inductances on both stator windings and rotor winding independent of rotor position will not develop a:

A. Synchronising torque

B. Starting torque

C. Reluctance torque

D. Hysteresis torque

22. The route of modern warfare has changed from the clash of large armies to suppression of innocent civilian population. Chemical agents are the biggest means and weapons for such warfare, and sadly enough there are people in the world who actually believe that chemical agents are helpful for this cause.

What sums up the meaning of the passage best?

A. Military establishment employees favour use of chemical weapons

B. Use of chemical weapons should be encouraged

C. Chemical agents have given a boom to modern warfare

D. Modern warfare has resulted in civil tremor

23. What 3-phase connection can be used to introduce a phase difference of 30o b/w output and input time voltages in a system?

A. Star Star

B. Star Delta

C. Delta Zig Zag

D. Delta Delta

24. Eq. circuit of a dedicated transformed contains leakage resistances X1, X2 and along with them magnetizing resistance XM. Magnitudes of these satisfy:

A. X1=X2<B. X1=X2>>XM

C. X1<>XM

D. X1>>X2>>XM

25. On a torque/speed curve in an induction motor there are 4 points of operation which are marked as W, X, Y and Z. In this which one of the points represents operation at slip more than 1?

1. X

2. Y

3. Z

4. W

26. In a logic gate all the inputs are 0 and the output is 1. The gate is:

A. NAND or XOR gate

B. NOR or XNOR gate

C. AND or XNOR gate

D. NOR or XOR gate

27. An AC voltage wave has been corrupted with n number of harmonics, in such a case overall voltage level is different from fundamental frequency components:

A. Only because of peak values

B. Only because of average values

C. Only because of rms values

D. All three(peak, rms and average value measures)

28. A DC motor which provides a dedicated zero speed regulation operating at full load without being connected to any controller is?

A. Differential Compound

B. Cumulative compound

C. Shunt

D. Series

29. In any transformer a 0 voltage regulation at full load is

A. Possible at lagging power factor load level

B. Possible at leading power factor load level

C. Possible at unity power factor load level

D. Not possible

30. In a transformer which statements can be considered valid?

A. In an open circuit test, current can be drawn out at low power factor.

B. In a short circuit test, current can be drawn out at 0 power factor.

C. In an open circuit test, current can be drawn out at high power factor.

D. In an open circuit test, copper losses are obtained while in the case of short circuit test core losses are obtained.

31. For a 1 phase induction motor (capacitor star) which of the following statements can be considered as valid?

A. Capacitor finds its use in power factor improvement

B. Direction of rotation can be altered by changing supply terminals

C. Direction of rotation cannot be altered

D. Direction of rotation can be changed by reversing main terminals

32. In any DC machine which of the following statements can be considered as true?

A. Compensating winding can be used for betterment of communication while interpole winding can be used for production of residual flux

B. Compensating winding can be used for improvement of communication while interpole winding can be used for neutralizing armature reaction

C. Compensating winding can be used for neutralizing armature reaction while interpole winding can be used for betterment of communication

D. Compensating winding can be used for neutralizing armature reaction while interpole winding can be used for production of residual flux

33. A capacitor is formed using polymeric dielectric having electric constant 2.26 and a dielectric breakdown strength measuring 50 KV/cm. Permittivity of free space is measured as 8.85 picoFarad/m. If the width of rectangular plates of capacitor are 20 cm and the length is 40cm find the maximum electric charge present in the capacitor:

A. 2microC

B. 4microC

C. 8microC

D. 10microC

34. A parallel plate capacitor has electrode area measure 100 mm2, there is a spacing of 0.1mm b/w the electrodes. A dielectric b/w plate of this capacitor is air which has permittivity of 8.85 x 10-12 F/m. Charge on capacitor is 100 V. What is the stored energy in the capacitor?

A. 440 picoJ

B. 22.1 picoJ

C. 44.3 nanoJ

D. 8.85 nanoJ

35 A zero mean random square value has been distributed uniformly having the limits –a and +a, the mean square value is equal to variance. RMS value of the signal is:

A. a/sqrt 3

B. a/sqrt 2

C. a x sqrt 2

D. a x sqrt 3

36. There is a lossy capacitor Cx which has been rated operating at 5kV, 50 Hz has been made into an equivalent circuit having an ideal capacitor Cp in parallel with a resistor Rp. Value of Cp is found to be 0.102 microF and value of Rp comes out to be 1.25 Mohm. Then find the power loss and tan eta of the lossy capacitor which is operating at rated voltage:

A. 10 W and 0.0002

B. 10 W and 0.0025

C. 20 W and 0.025

D. 20 W and 0.04

37. A unit step voltage is given to a R-L series circuit which has zero initial conditions at t=0. Which of the following statements can then be considered as correct?

A. It is possible that current is oscillatory

B. Resistor current will eventually fall to zero

C. Energy stored inside the inductor at steady state is considered as zero

D. Voltage across resistor at t=0+ is 0.

38. A passive 2 port network is kept in a steady state. When compared to the input, steady state output cannot offer:

A. Higher power

B. Lower impedance value

C. Better regulation

D. Highest voltage function

39. A voltage waveform V(t) = 12t2 is applied to an inductor worth 1H for t is greater than equal to 0, with initial conditions measured as 0. Current through inductor for this time period will be given as:

A. 12t

B. 24t

C. 4t3

D. 12t3

40. An electron which has a velocity u is placed inside an electric field E and a magnetic field B. force experienced by electron can be given as?

A. –Ee

B. –eu x B

C. –e(u x E +B)

D. –e(E + uxB)

41. For a scaler field u= x2 + y3 , what is the magnitude of gradient at point (1,3)

A. Sqrt(9)/2

B. Sqrt5

C. Sqrt(9)/3

D. 5

42. For the following eqn x” + 3x’(t) +2x(t) = 5, the solution x(t) approaches which values at t? infinity?

A. 5/2

B. 10

C. 5

D. 0

43. Two incandescent light bulbs of 40W and 60W are connected along mains in series:

A. 40W bulb glows brighter

B. Both bulbs glow at same level

C. 60W bulb glows brighter

D. Bulb together consume 100W

44. Inductance of a long solenoid 1000mm long which wounds up uniformly on a cylindrical tube of 60mm diameter at 3000 turns in milliH is:

A. 3.2

B. 32

C. 16

D. 1.6

45. Which of the following holds true for electric and magnetic field density divergence?

A. Both are zero

B. Zero for magnetic flux density

C. Zero for electric flux density

D. Zero for static densities but not zero for time varying density levels.

46. For a function f(x) = x2e-x which of the following occurs at x =?

A. 0

B. 1

C. -1

D. 2

47. A coin is tossed 3 times. If first toss gives a heads then what is the probabability of getting eaxtly two heads in 3 tosses?

A. 1/8

B. 3/8

C. 3/4

D. 1/2

48. A differential equation dx/dt = e-2tu(t) is to be solved making use of trapezoidal integration rule having a step size 0.01 seconds. Function u(t) gives a unit step function. Then find the value of X at t= 0.01 seconds given by

A. 0.00099

B. 0.0198

C. 0.0099

D. 0.00495