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C-DAC Electronics and Communication paper - Questions for placement

Here are a few questions asked in the technical round of C-DAC for Electronics and Communication students. It is observed that objective type questions are asked, where the students are expected to select the correct alternative.

1. What is High frequency transformer cores made of? 

(A) Graphite
(B) Mumetal
(C) Ferrite 
(D) Cast Iron 

2. What is used for high speed reading and storing of information in a computer?

(A) ferrite
(B) piezoelectric
(C) pyroelectrics
(D) ferromagnetics above 768

3. What are the poles of alternators made of?

(A) wrought iron
(B) permalloy
(C) CdS
(D) alnico

4. The change in a semi-conductor strain gauge, in resistance on application of strain is mainly due to the change in its

(A) length
(B) length and diameter
(C) resistivity
(D) diameter

5. Transformer oil is a liquid insulator and is mainly used in transformer. Why is it filled into transformer tank: 

I. To transfer the heat generated inside the transformer core and windings, to the outer cooling surfaces. II. To main insulation in the primary and secondary windings.

(A) Only I is correct
(B) Only II is correct
(C) Both I and II are correct 
(D) None of these

6. Which is the most malleable metal among the following?

(A) Au
(B) Ag 
(C) Cr
(D) Osmium

7. How are electrons in an atom visualized?

(A) spectroscopic techniques
(B) radiography 
(C) optical microscope
(D) etching techniques

8. As the temperature of a p-type semi-conductor is gradually and continuously increased, what will happen to the fermi level?

(A) into the valence band 
(B) into the conduction band
(C) towards the middle of the forbidden gap
(D) into the region between the acceptor level and the valence band

9. Which one of the following polarization mechanisms/sets of mechanisms contribute to the static dielectric constant of a homopolar neutral dielectric?

(A) Electric and dipplar
(B) Electronic and ionic
(C) Electronic, ionic and dipolar
(D) Electronic 

10. Consider the following materials:

1. Pure silica
2. Bakelite
3. Hard rubber
4. Paraffin

The correct sequence of the DECREASING order of loss angles (60 Hz) of these dielectric materials is

(A) 1,2,3,4
(B) 1,4,3,2
(C) 4,1,2,3
(D) 4,3,1,2 

11. Which material is piezoelectric?

(A) Pb2 Au
(B) NiFe2O4
(C) MgAl2O4
(D) BaTiO3

12. What happens to the residual resistivity of metals

(A) is essentially independent of temperature
(B) increases linearly with increasing temperature 
(C) decrease linearly with increasing temperature
(D) initially increase linearly with temperature and then remains constant

13. Consider the following metals:

1. Zinc
2. Gold
3. Silver
4. Copper

The correct sequence of the increasing order of their resistivity’s is

(A) 4,3,1,2
(B) 3,4,2,1
(C) 4,3,2,1
(D) 3,4,1,2

14. A type-I super-conductor maintained at a temperature T < Tc is subject to a magnetic field H< Hc. 

(A) partial diamagnetism 
(B) perfect diamagnetism
(C) perfect paramagnetism
(D) partial paramagnetism

15. What is the magnetic susceptibility of a paramagnetic material?

(A) less than zero
(B) less than one but positive 
(C) greater than one
(D) equal to zero

16. Consider the following statements: In a semi-conductor, the measurement of Hall co-efficient provides quantitative information on

1. Density of carriers
2. Polarity of carriers
3. Effective mass of the carriers
4. Mobility of the carriers

Of these statements :

(A) 1 and 2 are correct 
(B) 2 and 3 are correct
(C) 1 and 3 are correct
(D) 1,2,3 and 4 are correct

17. Silicon carbide reinforced aluminium metal matrix composites find application in

(A) the manufacture of transformer cores
(B) the manufacture of cutting tools
(C) the manufacture of standard resistors
(D) aerospace industry 

18. In what does the Gas Leds emit radiation?

(A) ultra-violet region
(B) violet-blue-green range of the visible region
(C) visible region
(D) infra-red region 

19. Which of the following pairs does-not match?

(A) Dielectric strength of air 3 to 5 kV/mm 
(B) Vacuum may be used for reflective insulation of liquid O2 tank 
(C) Permissible water content in transformer oil is 50 ppm 
(D) Carbon-pile resistors for insulation of oil-filled cables 

20. How can the memory of a computer be increased?

(A) increasing the magnetic bubble diameter 
(B) decreasing the magnetic bubble diameter 
(C) using strontium titanate (Sr Ti O3) 
(D) using adomax, a recent hard magnetic material

21. In what is the residual magnetic flux density more?

(A) Iron oxide
(B) Ceramic magnets 
(C) graphite 
(D) metallic magnets

22. What is 1:1 mixture in manganese ferrites? 

(A) MnO and CdO 
(B) MnO and Fe2O3 
(C) MnCl2 and Fe2O3 
(D) MnCl2 and CdO

23. Magnetostriction is a phenomenon whereby the magnetisation of a ferromagnetic material leads to a change in

(A) relative permeability
(B) physical dimensions 
(C) spontaneous magnetisation
(D) magnetic susceptibility

24. Two initially identical samples A and B of pure germanium are doped with donors to concentrations of 1*10, 20 m-3 and 3*10, 20 m-3 respectively. If the hole concentration in A is 9*10 12 m-3, then the hole concentration in B at the same temperature will be

(A) 3*10 12 m-3 
(B) 7*10 12 m-3
(C) 11*10 12 m-3
(D) 27*10 12 m-3

25. Consider the following statements: Pure germanium and pure silicon are examples of

1. Direct band-gap semi-conductors
2. Indirect band-gap semi-conductors
3. Degenrate semi-conductors of these statements

(A) 2 alone is correct
(B) 1 alone is correct 
(C) 3 alone is correct
(D) 1 and 3 are correct


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