As the temperature increases, the electrical resistance:
 1 decreases for conductors but increases for semiconductors. 2 increases for both conductors and semiconductors. 3 decreases for both conductors and semiconductors. 4 increases for conductors but decreases for semiconductors.
Subtopic: Â Energy Band theory |
Â 73%
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NEET - 2022
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In a semiconductor,

 (a) there are no free electrons at $$0~\text{K}.$$ (b) there are no free electrons at any temperature. (c) the number of free electrons increases with temperature. (d) the number of free electrons is less than that in a conductor.

Choose the correct option:
1. (a), (b)
2. (b), (c)
3. (a), (c), (d)
4. (a), (b), (d)
Subtopic: Â Energy Band theory |
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The band gap between the valence band and the conduction band in a certain material is $$3$$ eV. What is the longest wavelength of light that can create an electron-hole pair in the material, with the electron in the conduction band and the hole in the valence band? (Take $$hc$$ =$$1240$$ eV-nm.)
 1 $$414$$ nm 2 $$300$$ nm 3 $$830$$ nm 4 $$207$$ nm
Subtopic: Â Energy Band theory |
Â 87%
From NCERT
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Identify the incorrect statement from the following:
 1 The resistivity of a semiconductor increases with an increase in temperature. 2 Substances with an energy gap of the order of $$10$$ eV are insulators. 3 In conductors, the valence and conduction bands may overlap. 4 The conductivity of a semiconductor increases with an increase in temperature.
Subtopic: Â Energy Band theory |
Â 78%
From NCERT
AIPMT - 2005
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Carbon, Silicon, and Germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}},{}_{}$ ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$, and ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Ge}}$ respectively. Which one of the following relationships is true in their case?

1. ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}}<{\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Ge}}$

2. ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}}>{\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

3. ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}}={\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

4. ${\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{C}}<{\left({\mathrm{E}}_{\mathrm{g}}\right)}_{\mathrm{Si}}$

Subtopic: Â Energy Band theory |
Â 77%
From NCERT
AIPMT - 2005
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$$\mathrm{C}$$, $$\mathrm{Si}$$, and $$\mathrm{Ge}$$ have the same lattice structure. Why is the $$\mathrm{C}$$ insulator?

 1 because ionization energy for $$\mathrm{C}$$ is the least in comparison to $$\mathrm{Si}$$ and $$\mathrm{Ge}$$. 2 because ionization energy for $$\mathrm{C}$$ is highest in comparison to $$\mathrm{Si}$$ and $$\mathrm{Ge}$$. 3 the number of free electrons for conduction in $$\mathrm{Ge}$$ and $$\mathrm{Si}$$ is significant but negligibly small for $$\mathrm{C}$$. 4 both (2) and (3).

Subtopic: Â Energy Band theory |
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