Conduction Band

Q.

The conductivity of a pure semiconductor is roughly proportional to $T^{3/2}{e}^{-\Delta E/2KT}$ where $\Delta E$ is the band gap. The band gap for germanium is 0.74 eV at 4 K and 0.67 eV at 300 K. By what factor does the conductivity of pure germanium increase as the temperature is raised from 4 K to 300 K ?

Q.

Let $\Delta E$ denote the energy gap between the valence band and the conduction band. The population of conduction electrons (and of the holes) is roughly proportional to $e^{-\Delta E/2kT}.$ Find the ratio of the concentration of conduction electrons in diamond to that in silicon at room temperature 300 K. $\Delta E$ for silicon is 1.1 eV and for diamond is 6.0 eV. How many conduction electrons are likely to be in one cubic metre of diamond ?

Q.

The band gap between the valence and the conduction bands in zinc oxide (ZnO) is 3.2 eV. Suppose an electron in the conduction band combines with a hole in the valence band and the excess energy is released in the form of electromagnetic radiation. Find the maximum wavelength that can be emitted in this process.

Q. Indium antimonide has a band gap of $0.23\text{eV}$ between the valence and the conduction band. Find the temperature at which the thermal energy $kT$ equals the indium antimonide’s band gap.
$(k=\text{Boltzmann constant},T=\text{temperature})$
$(\text{Take}k=1.38\times {10}^{-23}{\text{JK}}^{-1})$

1. $1250\text{K}$
2. $1800\text{K}$
3. $2670\text{K}$
4. $3125\text{K}$

Q.

Calculate the number of states per cubic metre of sodium in 3s band. The density of sodium is $1013kg{m}^{-3}.$ How many of them are empty ?

Q. $1$ a.m.u (or u) = $1.66\times {10}^{-(20+x)}kg$. Find the value of $x$.

Q. Q 40/180 The de-Broglie wavelength of the electron inground state of a hydrogen atom is λ o. The radius of 4thorbit of hydrogen atom in terms of A

Q. Two block of mass $10kg$ and $20kg$ is separated by a distance $100km$. What is the gravitational field (F) if $G=6.67408\times {10}^{-11}{m}^{3}k{g}^{-1}{s}^{-2}$?

1. $13.34\times {10}^{-16}N$
2. $1334\times {10}^{-16}N$
3. $1.334\times {10}^{-18}N$
4. $1.334\times {10}^{-11}N$

Q. If threshold frequency of a metal surface is $7\times {10}^{14}\text{Hz}$, find the work function of the metal.

1. $2.2\text{eV}$
2. $4.6\text{eV}$
3. $2.9\text{eV}$
4. $9.2\text{eV}$

Q. The de-Broglie wavelength of the electron in ground state of a hydrogen atom is λ . The radius of 4th orbit of hydrogen atom in terms of λ is?

Q. How many moles are there in 1 $metr{e}^3$ of any gas at NTP?

Q. The figure shows two conducting concentric sperical shells of radii R and 2R.
The inner shell has a charge +Q and the outer one is neutral.

(A)	Energy stored in region given by R < r < 2R	P) $\frac{Q^2}{32\pi {ϵ}_{o}R}$
(B)	Energy stored in region given by $2R<r<\infty$	Q) $\frac{Q^2}{16\pi {ϵ}_{o}R}$
(C)	Energy stored in region given by 2R < r < 4R	R) $\frac{Q^2}{8\pi {ϵ}_{o}R}$
(D)	Heat generated when switch S is closed	S) zero

T) None

1. A $\to$ Q, B $\to$ Q, C $\to$ P, D $\to$ Q,
2. A $\to$ R, B $\to$ Q, C $\to$ S, D $\to$ S,
3. A $\to$ R, B $\to$ R, C $\to$ P, D $\to$ Q,
4. A $\to$ Q, B $\to$ R, C $\to$ S, D $\to$ S,

Q.

Number of secondary electrons emitted per number of primary electrons depends on [RPET 2000]

1. Material of target

2. Intensity

3. None of the above

4. Frequency of primary electrons

Q. Define the activity of a given radioactive substance. write its S.I units