# Electronics and Communication Engineering - Materials and Components

### Exercise :: Materials and Components - Section 3

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

Explanation:

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37.

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

 A. 2p∈0R B. 4p∈0R C. 4p∈0R2 D. 4p 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|

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. 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