Band Theory and Types of Solids

Q.

Why does the electrical conductivity of semiconductors increase with rise in temperature ?

Q.

In terms of band theory, what is the difference

(i) Between a conductor and an insulator ?

(ii) Between a conductor and a semiconductor ?

Q.

The energy gap between the conduction band and valence band is of the order of $0.07eV$. It is a/an

1. insulator

2. conductor

3. semiconductor

4. alloy

Q.

What type of solids are electrical conductors, malleable and ductile?

Q. The conductivity of a semiconductor can be increased by:

1. Heating the semiconductor
2. Doping the semiconductor with electron rich impurity
3. Doping the semiconductor with electron deficient impurity
4. All of the above

Q. The energy gap in a conductor at room temperature is ____.

1. greater than that in a semiconductor
2. less than that in a insulator
3. greater than that in a insulator
4. Both (A) and (B) are true

Q.

Which of the following oxides behaves as conductor or insulator depending upon temperature ?

(a) TiO (b) $Si{O}_2$ (c) $Ti{O}_3$ (d) MgO

Q. Assertion: Electrical conductivity of semiconductors decreases with increasing temperature.
Reason: With increase in temperature, large number of electrons from the valence band can jump to the conduction band.

1. If both assertion and reason are true but reason is not the correct explanation of the assertion.
2. If assertion Is false but reason is true.
3. If assertion is true but reason is false.
4. If both assertion and reason are true and the reason is the correct explanation of the assertion.

Q. For n-type semiconductor fermi level is near the conduction band.

1. True
2. False

Q.

With rise in temperature the electrical conductivity of intrinsic semiconductor __.

1. Increases

2. Decreases

3. First increases and then decreases

4. First decreases and then increases

Q.

Which of the following solids is not an electrical conductor ?

1. Mg(s) 2.Tio(s) 3.$I_2$ (s) 4. $H_{2}O$ (s)

(a) Only 1 (b) Only 2 (c) 3 and 4 (d) 2, 3 and 4

Q.

‘X’ melts at low temperature and is a bad conductor of electricity in both liquid and solid state. X is:

1. Mercury

2. Silicon Carbide

3. Zinc Sulphide

4. Carbon Tetrachloride

Q.

Which of the following statements are true about metals ?

(a) Valence band overlaps with conduction band

(b) The gap between valence band and conduction band is negligible

(c) The gap between valence band and conduction band connot be determined

(d) Valence band may remain partially filled

Q.

Example for valence band and conduction band

Q. Which of the following represents correct order of conductivity in solids?

1. metals< insulators < semiconductors
2. metals insulators
3. metals > insulators< semiconductors
4. metals >semiconductors >insulators

Q. Metals are good conductors of electricity because

1. They are malleable and ductile

2. They are very dense solids

3. They are held by strong forces

4. They have mobile electrons

Q.

Give reason for the statement “ Gold has a variable valency”.

Q.

The material used for coating on electric wires to avoid electric shock is __________.

1. conductor

2. insulator

3. semiconductor

4. superconductor

Q.

In the following questions a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct answer out of the following choices.

(a) Assertion and Reason both are correct statements an Reason is correct explanation for Assertion.

(b) Assertion and Reason both are correct satements but Reason is not correct explanation for Assertion.

(c) Assertion is correct statement but Reason is wrong statement

(d) Assertion is wrong statement but Reason is correct statement.

Assertion (A) Semiconductors are solids with conductivities in the intermediate range from ${10}^{-}6-{10}^{4}oh{m}^{-}1m^{-}1$.

Reason (R) Intermediate conductivity in semiconductor is due to partially filled valence band.

Q. Which among the following solids are electrical insulators in solid state:

1. Non polar molecular solids
2. All of above
3. Polar molecular solids
4. Ionic solids

Q. Which of the following statement is correct regarding band theory?

1. For semiconductors, small energy gap is there between conduction band and valence band
2. For insulators, large energy gap is there between conduction band and valence band
3. All of the above.
4. For conductors, no energy gap is there between conduction band and valence band

Q.

Which of the following property is not responsible for copper to be used as electrical conduction wires?

1. Ductility

2. Color

3. Good conductor of electricity

4. It is solid

Q.

What is the order of Band gap in the following materials?

1. Insulator> Semiconductors>Conductors

2. Conductors>Semiconductors> Insulators

3. Semiconductors>Conductors> Insulators

4. Conductors>Insulators> Semiconductors

Q. Metals are good conductors of electricity because

1. They are malleable and ductile
2. They are very dense solids
3. They are held by strong forces
4. They have mobile electrons

Q. What is the order of Band gap in between substances given below. Silver, silicon, glass.

1. Silver > glass > silicon

2. Silver>Silicon>glass

3. glass>Silicon>Silver

4. glass>Silver>silicon

Q.

What is a semiconductor? Describe the two main types of semiconductors and contrast their conduction mechanism.

Q.

An intrinsic semi-conductor will behave similar to an insulator at T = 0 K .Why?

Q.

Give the reasons why copper metal is used for making electric wires.

Q.

An n-type semiconductor is

1. neutral

2. positively charged

3. negatively charged

4. negatively or positively charged depending in the impurity added.

Q. Why the conductivity of metals decreases with increase in temperature??