Energy Band Diagrams

Q.

What is the energy band gap of silicon and germanium respectively in eV?

1. $1.1,0.7$

2. $0.7,1.1$

3. $-0.7,-1.1$

4. $-1.1,-0.7$

Q. Pure Si at $300K$ has equal electron and hole concentration of $1.5\times {10}^{16}/m^3$. Doping by indium increases $n_h$ to $4.5\times {10}^{22}/m^3$. What is $n_e$ in doped silicon?

1. $5\times {10}^9/m^3$
2. $1.5\times {10}^{16}/m^3$
3. $4.5\times {10}^{22}/m^3$
4. $4.5\times {10}^{16}/m^3$

Q. The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 $nm$ is incident on it. The band gap in ($eV$) for the semiconductor is

1. 1.1 $eV$
2. $2.5eV$
3. $0.5$ $eV$
4. $0.7$ $eV$

Q. What is the difference between conductivity and mobility?

Q.

Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to (Eg)C, (Eg)Si and (Eg)Ge. Which of the following statements is true? (a) (Eg)Si < (Eg)Ge < (Eg)C

(b) (Eg)C< (Eg)Ge > (Eg)Si

(c) (Eg)C> (Eg)Si > (Eg)Ge

(d) (Eg)C= (Eg)Si = (Eg)Ge

Q. A red LED emits light at $0.1$ Watt uniformly around it. The amplitude of the electric field of the light at a distance of $1m$ from the diode is

1. $6V/m$
2. $2.45V/m$
3. $5.48V/m$
4. $1.73V/m$

Q.

The power factor of a good choke coil is

1. Nearly zero

2. Exactly zero

3. Nearly one

4. Exactly one

Q. Depletion layer consists of:

1. Electron
2. Proton
3. Mobile ions
4. Immobile ions

Q.

What is the forbidden energy gap or band gap?

1. conduction band

2. when there is no energy

3. the forbidden energy gap is the difference between energy levels of the conduction band and within the conduction band.

4. the forbidden energy gap is the difference in energy levels of the conduction band and valence band

Q.

The band gap for silicon is 1.1 eV. (a) Find the ratio of the band gap to kT for silicon at room temperature 300 K. (b) At what temperature does this ratio become one tenth of the value at 300 K ? (Silicon will not retain its structure at these high temperatures.)

Q. what is unipositive and uninegative ions

Q. In NaCl the centers of two nearest like charged ion are present at a distance of.

Q. In photoelectric effect, if a weak intensity radiation instead of strong intensity of suitable frequency is used then a) Photoelectric effect will get delayed. b) Photoelectric effect will not take place. c) Saturation current will decrease

Q.

A step-down transformer transforms a supply line voltage of $2200V$ into $220V$. The primary coil has $5000$ turns. The efficiency and power transmitted by the transformer are $90\%$ and $8kW$ respectively. Then, the power supplied is

1. $9.89kW$

2. $8.89kW$

3. $88.9kW$

4. $889kW$

Q.

Which of the following controls the flow of current in a circuit?

1. resistor

2. switch

3. battery

4. both (a) and (b)

Q.

What does band gap mean?

Q.

How did Sommerfeld explain the fine structure of hydrogen spectrum?

Q.

factors affecting Internal Resistance.

Q.

Evaluate Rydberg constant by putting the values of the fundamental constants in its expression.

Q. 18.What does the term the resistivity of copper is 1.69*10-8 refers to

Q.

What is the purpose of using charcoal and salt mixture near the copper plate that is buried in the ground?

Q. ntWhen KI is added to AgNO3 solution then why in the electrical double layer of AgI, diffuse layer is of I- ion and not of NO3- ion?n ntn

Q. A semiconductor X is made by doping a germanium crystal with arsenic ($Z=33$). A second semiconductor Y is made by doping germanium with indium ($Z=49$). These two are joined end to end and connected to a battery as shown. Which of the following statements is correct?

1. X is P-type, Y is N-type and the junction is forward biased
2. X is N-type, Y is -type and the junction is forward biased
3. X is P-type, Y is N-type and the junction is reverse biased
4. X is N-type, Y is P-type and the junction is reverse biased

Q.

Why do band gaps exist?

Q. Explain the formation of energy bands in solids. On the basis of energy bands distinguish between a metal, a semiconductor and an insulator.

Q. A p-n photodiode is fabricted from a semiconductor with a band gap of 2.5eV. It can detect a signal of wavelength

1. 6000
2. 6000 nm
3. 4000
4. 4000 nm

Q. In an intrinsic semiconductor we doped boronwith density 1.5 x 1018 atoms/cm3 andposphorus with density 1018 atoms/cm3 thernwhich type of semiconductor forms and whatis the charge carrier density(1) P-type, 0.5 x 1018 cm-3(2) N-type, 0.5 × 1018 cm-3(3) P-type, 2.5 x 1018 cm-3(4) N-type, 2.8 x 1018 cm

Q.

Can two electrons have the same quantum numbers?

Q.

Where is direct current used?

Q.

The conductivity of a photosensitive semiconductor depends on?