Mechanism of Carrier Conduction

Q. What is the net charge on the semiconductor when it is doped with;
1) N type semiconductor
2)P type semiconductor
The answer for both cases is zero because it is neutral. But how it be neutral when it has excess electrons (when doped with n type) or holes ( when doped with p type) ??

Q.

Which of the following is ferromagnetic?

1. $\mathrm{Fe},\mathrm{Co},\mathrm{Ni}$

2. $\mathrm{Cu},\mathrm{Ag},\mathrm{Au}$

3. $\mathrm{Ca},\mathrm{Sr},\mathrm{Ba}$

4. $\mathrm{Zn},\mathrm{Cd},\mathrm{Hg}$

Q. A paisa coin is made up of Al - Mg alloy and weighs 0.75 g. It has a square shape and its diagonal measures 17 mm. It is electrically neutral and contains equal amounts of positive and negative charges. Treating the paisa coins made up of only Al, find the magnitude of equal number of positive and negative charges. What conclusion do you draw from this magnitude?

Q. A silicon specimen is made into a$P-$type semiconductor by doping, on an average, one Indium atom per $5\times {10}^7$silicon atoms. If the number density of atoms in the silicon specimen is$5\times {10}^{28}{\text{per m}}^3$. Then the number of acceptor atoms in silicon per cubic centimetre will be,

1. $2.5\times {10}^{30}{\text{per cm}}^3$
2. $1.0\times {10}^{13}{\text{per cm}}^3$
3. $1.0\times {10}^{15}{\text{per cm}}^3$
4. $2.5\times {10}^{36}{\text{per cm}}^3$

Q.

Mobilities of electrons and holes in a sample of intrinsic germanium semiconductor
at room temperature are 0.36m²/volt-sec and 0.17 m²/volt-sec respectively. If the electron and hole densities are each equal to 2.5 X 10¹⁹/m³, the conductivity is.

1. 4.12 S/m

2. 2.12 S/m

3. 1.22 S/m

4. 3.12 S/m

Q.

How does current flow in a PNP transistor?

Q.

In a pure semiconductor, the number of conduction electrons is $6\times {10}^{19}$ per cubic metre. How many holes are there in a sample of size $1cm\times 1cm\times 1mm?$

Q. Is there any lower limit to the electric force between two particles placex at a separation of 1 cm. Explain your answer

Q. what are the number of electrons protons and neutrons present in a alpha particle, beta particle, gamma particle, neutrino and antineutrino

Q. The valence band of a semiconductor at 0 K is

1. completely filled
2. completely empty
3. partially filled
4. nothing can be said

Q. A metallic particle having no net charge is placed near a finite metal plate carrying a positive charge. The electric force on the particle will be

1. towards the plate
2. away from the plate
3. parallel to the plate
4. zero

Q.

What is the difference between diffusion current and drift current?

Q.

In n-type semiconductors majority charge carriers are

Q. a capacitor is connected across a battery which delivers a current o 1 A at an instant in the capacitor . Displacement current through the capacitor at that instant is

Q. Four charges q1=1, q2=2, q3=3and q4=4 in microcolumb are placed at(0, 0, 0), (1m, 0, 0), (0, 1m, 0), (0, 0, 1m) respectively. Let Fi be the net force acting on ith charge of the given charge then sigmaFi=

Q.

How does the internal resistance increase?

Q.

In a semiconductor, separation between conduction and valence band is of the order of

1. $100eV$

2. $10eV$

3. $1eV$

4. $0eV$

Q.

What is the reason for positive charge on a sodium ion and a negative charge on a chloride ion in the formation of Sodium chloride?

Q.

Name the following:

Two ferromagnetic substances.

Q. what is the donor concentration in n-type germanium of 1ohm-cm resistivity at 300K given electron mobility is equals to 3900cm^{}/V.s

Q. How electron hole pairs are generated in p-n junction ?

Q.

The drift current in a p-n junction is $20.0\mu A.$ Estimate the number of electrons crossing a cross section per second in the depletion region.

Q. Why zener diode is not used in forward biasing?

Q.

A semiconducting material has a band gap of 1 eV. Acceptor impurities are doped into it which create acceptor levels 1 me V above the valence band. Assume that the transition from one energy level to the other is almost forbidden if kT is less than 1/50 of the energy gap. Also, if k T is more than twice the gap, the upper levels have maximum population. the temperature of the semiconductor is increased from 0 K. the concentration of the holes increases with temperature and after a certain temperature it becomes approximately constant. As the temperature is further increased, the hole concentration again starts increasing at a certain temperature. Find the order of the temperature range in which the hole concentration remains approximately constant.

Q. what is reverse current and what is reverse saturation current during reversed bias condition?

Q. What n - type semiconductor is heated :

1. number of electrons increases while that of holes decreases
2. number of holes increases while that of electrons decreases
3. number of electrons and holes increase equally.
4. number of electrons and holes increase equally
5. none of these

Q.

What is the difference between semiconductors and transistors?

Q.

What is the best semiconductor ?

1. Wood

2. Paper

3. Silicon

4. Copper

Q.

After arriving at saturation current further increase in anode potential does not change in magnitude of current why?

Q.

If the ratio of concentration of electrons to that of holes in a semiconductors is $\frac{7}{5}$ and the ratio of currents is $\frac{7}{4}$, what is the ratio of their drift velocities?

1. $\frac{5}{8}$

2. $\frac{4}{5}$

3. $\frac{5}{4}$

4. $\frac{4}{7}$