Regarding a semiconductor which one of the following is wrong 

(1) There are no free electrons at room temperature

(2) There are no free electrons at 0 K

(3) The number of free electrons increases with rise of temperature

(4) The charge carriers are electrons and holes

Which of the following statements is true for an N-type semi-conductor 

(1) The donor level lies closely below the bottom of the conduction band

(2) The donor level lies closely above the top of the valence band

(3) The donor level lies at the halfway mark of the forbidden energy gap

(4) None of above

Choose the correct statement

(1) When we heat a semiconductor its resistance increases

(2) When we heat a semiconductor its resistance decreases

(3) When we cool a semiconductor to 0 K then it becomes super conductor

(4) Resistance of a semiconductor is independent of temperature

Intrinsic semiconductor is electrically neutral. Extrinsic semiconductor having large number of current carriers would be 

(1) Positively charged

(2) Negatively charged

(3) Positively charged or negatively charged depending upon the type of impurity that has been added

(4) Electrically neutral

If ${\mathrm{n}}_{\mathrm{e}}$ and ${\mathrm{v}}_{\mathrm{d}}$ be the number of electrons and drift velocity in a semiconductor. When the temperature is increased

(1) ${\mathrm{n}}_{\mathrm{e}}$ increases and ${\mathrm{v}}_{\mathrm{d}}$ decreases

(2) ${\mathrm{n}}_{\mathrm{e}}$ decreases and ${\mathrm{v}}_{\mathrm{d}}$ increases

(3) Both ${\mathrm{n}}_{\mathrm{e}}$ and ${\mathrm{v}}_{\mathrm{d}}$ increases

(4) Both ${\mathrm{n}}_{\mathrm{e}}$ and ${\mathrm{v}}_{\mathrm{d}}$ decreases

The energy gap of silicon is 1.14 eV. The maximum wavelength at which silicon will begin absorbing energy is

(1) 10888 Å                   

(2) 1088.8 Å

(3) 108.88 Å                   

(4) 10.888 Å

Which of the following energy band diagram shows the N-type semiconductor

1. 

2. 

3. 

4. 

The mobility of free electrons is greater than that of free holes because

1. They carry negative charge

2. They are light

3. They mutually collide less

4. They require low energy to continue their motion

The electron mobility in N-type germanium is 3900 ${\mathrm{cm}}^2$/v-s and its conductivity is 6.24 mho/cm, then impurity concentration will be if the effect of cotters is negligible
(a) ${10}^{15} /{\mathrm{cm}}^3$                  (b) ${10}^{13}/{\mathrm{cm}}^3$
(c) ${10}^{12}/{\mathrm{cm}}^3$                   (d) ${10}^{16}/{\mathrm{cm}}^3$

Which of the energy band diagrams shown in the figure corresponds to that of a semiconductor

1. 

2. 

3. 

4.