Electronics and Communication Engineering - Materials and Components

36. 

Assertion (A): For most metals, Fermi energy EF is less than 10 eV.

Reason (R): Fermi level of a metal is given by EF = 3.64 x 10-19 (n)2/3 where n is number of free electrons/m3 of metal.

A. Both A and R are true and R is correct explanation of A
B. Both A and R are true but R is not correct explanation of A
C. A is true but R is false
D. A is false but R is true

Answer: Option A

Explanation:

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37. 

The capacitance of an insulated conducting sphere of radius R in vacuum is

A. 2p0R
B. 4p0R
C. 4p0R2
D. 4p

Answer: Option B

Explanation:

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38. 

The transition of electron from energy level W1 to W2 is associated with emission or absorption of electro magnetic radiation of frequency f such that

A. hf = |W1 - W2|
B. |W1 - W2|f = h
C. hf = 0.5|W1 - W2|
D. (hf)2 = |W1 - W2|

Answer: Option A

Explanation:

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39. 

A material has N spins per m3. If Np are the dipoles per m3 parallel to field and Na are the dipoles per m3 anti-parallel to field, the magnetisation is

A.
B.
C.
D.

Answer: Option A

Explanation:

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40. 

Even at room temperature, an intrinsic semiconductor has some holes. These holes are due to

A. electron
B. doping
C. thermal energy
D. free electrons

Answer: Option C

Explanation:

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