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Q. No.An electric field is applied to a semiconductor. Let the number of charge carriers be \(n\) and the average drift speed be \(v.\) If the temperature is increased, then:
| 1. | both \(n\) and \(v\) will increase. |
| 2. | \(n\) will increase but \(v\) will decrease. |
| 3. | \(v\) will increase but \(n\) will decrease. |
| 4. | both \(n\) and \(v\) will decrease. |
Subtopic: Â Types of Semiconductors |
Level 3: 35%-60%
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In a semiconductor;
| (A) | there are no free electrons at \(0^\circ\text{K}.\) |
| (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 from the given ones:
| 1. | (A) and (B) only |
| 2. | (B) and (C) only |
| 3. | (A), (C), and (D) only |
| 4. | (A), (B), and (D) only |
Subtopic: Â Energy Band theory |
 86%
Level 1: 80%+
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A piece of iron and a piece of germanium are cooled from the \(400~\text{K}\) temperature down to \(77~\text{K}\).
Then:
Then:
| 1. | the resistance of each of them increases |
| 2. | the resistance of each of them decreases |
| 3. | the resistance of iron increases and that of germanium decreases |
| 4. | the resistance of iron decreases and that of germanium increases |
Subtopic: Â Types of Semiconductors |
 75%
Level 2: 60%+
Please attempt this question first.
Hints
Please attempt this question first.
Choose the only false 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 \(10~\text{eV}\) 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 |
 82%
Level 1: 80%+
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Please attempt this question first.
Let \(n_{p}\) and \(n_{e}\) be the number of holes and conduction electrons in an intrinsic semiconductor. Then:
1. \(n_{p}> n_{e}\)
2. \(n_{p}= n_{e}\)
3. \(n_{p}< n_{e}\)
4. \(n_{p}\neq n_{e}\)
Subtopic: Â Types of Semiconductors |
 84%
Level 1: 80%+
Hints
Hole is:
| 1. | an anti-particle of electron. |
| 2. | a vacancy created when an electron leaves a covalent bond. |
| 3. | absence of free electrons. |
| 4. | an artificially created particle. |
Subtopic: Â Types of Semiconductors |
 89%
Level 1: 80%+
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The conductivity of a semiconductor increases with an increase in temperature,
because:
because:
| 1. | number density of free current carries increases |
| 2. | relaxation time increases |
| 3. | both number density of carries and relaxation time increase |
| 4. | number density of current carriers increases, relaxation time decreases but the effect of decrease in relaxation time is much less than the increase in number density |
Subtopic: Â Energy Band theory |
 77%
Level 2: 60%+
Hints
Given below are two statements:
| Assertion (A): | The temperature coefficient of resistance is positive for metals and negative for \(\mathrm{p\text-}\)type semiconductors. |
| Reason (R): | The effective charge carriers in metals are negatively charged whereas in \(\mathrm{p\text-}\)type semiconductors, they are positively charged. |
| 1. | Both (A) and (R) are True and (R) is the correct explanation of (A). |
| 2. | Both (A) and (R) are True but (R) is not the correct explanation of (A). |
| 3. | (A) is True but (R) is False. |
| 4. | Both (A) and (R) are False. |
Subtopic: Â Energy Band theory |
 54%
Level 3: 35%-60%
Please attempt this question first.
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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 |
 74%
Level 2: 60%+
Hints
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 |
 75%
Level 2: 60%+
NEET - 2022
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