Carrier Concentration

Q. 126.Two electrons lying 10 cm apart are released. What will be their speed when they are 20 cm apart?

Q.

A p-type semiconductor has acceptor levels 57 $meV$ above the valence band. The maximum wavelength of light required to create a hole is (Planck's constant

h= 6.6×10-34J-s)

1. 57 Å
2. 57×10-3 Å
3. 217100 Å
4. 11.61×10-33Å

Q.

What is the value of the energy gap in semiconductors?

Q.

Two electrons are moving toward each other each with a velocity of ${10}^6$ m/s what will be the closest distance of approach between them.

Q.

Why is silicon a semiconductor?

Q.

Show on a graph, the variation of resistivity with temperature for a typical semiconductor.

Q. Highly excited states for hydrogen like atoms (also called Rydberg states) with nuclear charge $Ze$ are defined by their principal quantum number $n,$ where $n>>1$. Which of the following statement(s) is(are) true ?

1. Relative change in the radii of two consecutive orbitals does not depend on $Z$
2. Relative change in the radii of two consecutive orbitals varies as $1/n$
3. Relative change in the energy of two consecutive orbitals varies as $1/n^3$
4. Relative change in the angular momenta of two consecutive orbitals varies as $1/n$

Q. What are $\alpha$ and $\beta$ parameters for a transistor? Obtain a relation between them.

Q. If $n_e$ and $v_d$ be the number of electrons per unit volume and drift velocity of the electrons, in a semiconductor. When its temperature is increased,

1. only $n_e$ decreases
2. only $n_e$ increases
3. both $n_e$ and $v_d$ increases
4. both $n_e$ and $v_d$ decreases

Q. The net charge on a capacitor is

Q. If we add impurities in semiconductor than the number of electrons in conduction band increase is this imply that the semiconductor with impurities will conduct more electricity? Or the electricity remains same?

Q. Three large conducting plates 1, 2 and 3 are kept close to each other and are given charges Q, 3Q and 5Q respectively. Now plates 1 and 2 are connected to each other by a thin conducting wire. Find the charge on each face of ech plate.

Q.

What happens when a forward bias is applied to a p-n junction?

Q. Why are charges independent of mass

Q. The number of silicon atoms per m3is 5 × 1028. This is dopedsimultaneously with 5 × 1022 atoms per m3of Arsenic and 5 × 1020per m3atoms of Indium. Calculate the number of electrons and holes.Given that ni= 1.5 × 1016 m–3. Is the material n-type or p-type?

Q. 5.The ratio of the lengths, densities, masses and resistivities of two wires A and B are 1: 2, 1: 2, 1:1, 1: 4 respectively. The ratio of their resistance are:

Q. The time period of revolution of $e^{-}$ in ground state orbit of hydrogen atom is $T_{\lambda }$, then frequency of $e^{-}$ in second excited state of $L{i}^{++}$ ion is

1. $\frac{1}{3T}$
2. $\frac{1}{8T}$
3. $\frac{9}{T}$
4. $\frac{9}{8T}$

Q. 39. A point charge Q = -8 nC is located at the origin. The electric field at the point x=1.2 m and y=-1.6 m as shown in the figure is

Q. An intrinsic semiconductor has ${10}^{18}/m^3$ free electron and is doped with pentavalent impurity of ${10}^{24}/m^3$. Then the free electrons density order increase by

1. $4$
2. $3$
3. $6$
4. $5$

Q. The electron density of intrinsic semiconductor at room temperature is ${10}^{16}$ $m^{-3}$. When doped with a trivalent impurity, the electron density is decreased to ${10}^{14}$ $m^{-3}$ at the same temperature. The majority carrier density is:

1. ${10}^{16}{m}^{-3}$
2. ${10}^{18}{m}^{-3}$
3. ${10}^{21}{m}^{-3}$
4. ${10}^{20}{m}^{-3}$
5. ${10}^{19}{m}^3$

Q. 52.Calculate the debroglie wavelength of the electron orbiting in the n=2 states of hydrogen atom

Q. 10.Find the charge on 3 micro farad , 4 micorfarad and 5 micro farad. Also find the potential of point C and D.

Q. The wavelength of radiation emitted is Y when an electron jumps from third to second orbit of hydrogen atom for the electron to jump from the fourth to the second orbit of the hydrogen atom the wavelength of radiation emitted will be

Q. Pure $Si$ at $500K$ has equal number of electron $\left(n_e\right)$ and hole $\left(n_h\right)$ concentration of $1.5\times {10}^{16}{m}^{-3}$. Doping by indium increases $n_h$ to $4.5\times {10}^{22}{m}^{-3}$. The doped semiconductor is of

1. $n$-type with electron concentration $n_e=5\times {10}^{22}{m}^{-3}$
2. $p$-type with electron concentration $n_e=2.5\times {10}^{10}{m}^{-3}$
3. $p$-type having electron concentrations $n_e=5\times {10}^9{m}^{-3}$
4. $n$-type with electron concentration $n_e=2.5\times {10}^{23}{m}^{-3}$

Q. The mobility of free electron is greater than that of three holes because

Q. In a semiconductor, it is found that $\frac{3}{5}th$ of the total current is carried by electrons and the remaining $\frac{2}{5}th$ by the holes. If at this temperature, the drift speed of electrons is $2.5$ times that of holes, the ratio of the number densities of electrons and holes is

1. $\frac{3}{5}$
2. $\frac{5}{8}$
3. $\frac{25}{8}$
4. $\frac{1}{2}$

Q. When will the conductivity of a Germanium semiconductor decrease?

1. On adding donor impurity
2. On adding acceptor impurity
3. On decreasing the temperature
4. In making UV light incident

Q. The resistivities of wire at 20°C & 100°C are 3 ohm m & 4 ohm m respectively. Find the resistivity of wire at 0°C.

Q. The temperature $\left(T\right)$ and dependence of resistivity $\left(\rho \right)$ of a semiconductor is represented by,

1. 
2. 
3. 
4. 

Q. When the temperature of a n-type semiconductor is increased :

1. Minority carriers are decreased
2. Net negative charge is increased
3. Net charge is zero
4. None of the above is true