Electronics and Communication Engineering - Electronic Devices and Circuits

11. 

At very high temperatures the extrinsic semi conductors become intrinsic because

A. drive in diffusion of dopants and carriers
B. band to band transition dominants over impurity ionization
C. impurity ionization dominants over band to band transition
D. band to band transition is balanced by impurity ionization

Answer: Option B

Explanation:

Covalent bonds are broken.


12. 

When a voltage is applied to a semiconductor crystal then the free electrons will flow.

A. towards positive terminal
B. towards negative terminal
C. either towards positive terminal or negative terminal
D. towards positive terminal for 1 μs and towards negative terminal for next 1 μs

Answer: Option A

Explanation:

Since electrons are negatively charged they will flow towards positive terminal.


13. 

Ferrite have

A. low copper loss
B. low eddy current loss
C. low resistivity
D. higher specific gravity compared to iron

Answer: Option C

Explanation:

Ferrite is a low density material of composition with Fe2O3 x O, where x is a bivalent metal, such as Cobart, Ni, Mn. These magnetic materials having very low loss of current and used in high frequency circuit.


14. 

In a p type material the Fermi level is 0.3 eV above valence band. The concentration of acceptor atoms is increased. The new position of Fermi level is likely to be

A. 0.5 eV above valence band
B. 0.28 eV above valence band
C. 0.1 eV above valence band
D. below the valence band

Answer: Option B

Explanation:

Addition of acceptor atom brings Fermi level closer to valence band.


15. 

In an n-p-n transistor, the majority carriers in the base are

A. electrons
B. holes
C. both holes and electrons
D. either holes or electrons

Answer: Option A

Explanation:

Emitter is n type and emits electrons which diffuse through the base.