Semiconductor Electronics: Materials, Devices and Simple Circuits Test 28

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Semiconductor Electronics: Materials, Devices and Simple Circuits Test 28

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Weekly Quiz Competition

Question 1
1 / -0

The conductivity of a magnetic substance for the lines of force with respect to air is called the

A
Magnetic induction

B
Magnetic permeability

C
Magnetic flux density

D
Intensity of magnetisation

Solution
Question 2
1 / -0

Which of the following doping will produce a p-type semiconductor?

A
Germanium with phosphorus

B
Silicon with germanium

C
Germanium with antomony

D
Silicon with indium

Solution

The p-type semiconductor is formed by doping either Si or Ge with a trivalent atom. Out of given options, only indium is a trivalent atom.
So, a p-type semiconductor is formed by using silicon with indium.
Question 3
1 / -0

The most widely used semiconductors are
(i) silicon (ii) germanium
(iii) phosphorus (iv) arsenic

A
(i) and (ii)

B
(ii) and (iii)

C
(iii) and (iv)

D
(i), (ii), (iv),(iii)

Solution

Si and Ge are most widely used semiconductors because of their atomic structures. They have 4 electrons in valence shell which forms four covalent bonds with neighboring atoms in crystal lattice which can be altered by adding dopants.
Whereas, phosphorus and arsenides are dopants added to a pure semiconductor to increase their conductivity.
Question 4
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Electrical conduction in a semiconductor takes place due to

A
electrons only

B
holes only

C
both electrons and holes

D
neither electrons nor holes

Solution

A semiconductor has two types of charge carriers i.e. holes and electrons. The conductivity of a semiconductor is sum of conductivities of holes and electrons i.e. $$\sigma =en_{i}(\mu _{h}+\mu _{e})$$.
where, $$n_{i}$$ = intrinsic concentration
$$\mu _{h}$$ = mobility of holes
$$\mu _{e}$$= mobility of electrons
Therefore, electrical conduction in a semiconductor is due to holes and electrons both.
Question 5
1 / -0

In a $$p$$-type semi-conductor, the majority carriers are

A
Protons

B
Electrons

C
Holes

D
Positive ions

Solution
Question 6
1 / -0

Space charge region around a p-n junction:

A
does not contain mobile carriers

B
contains both free electrons and holes

C
contains one type of mobile carriers depending on the level of doping

D
contains electrons only as free carriers

Solution

Space charge region around p-n junction also known as depletion region. The depletion layer is called so, as it is depleted of mobile carriers. Space charge regions contain fixed position of negative and positive space charge regions on either side of p-n junction i.e. on p and n side of junction respectively. These space charge regions are static, i.e. contain immobile carriers.
Question 7
1 / -0

In a p-type semiconductor majority charge carriers are _________.

A
holes

B
electrons

C
both holes and electrons

D
ions

Solution

In the p-type semiconductor, the holes are in abundance as compared to electrons. The charge carriers in abundance are called majority charge carriers. So, holes are majority charge carriers in a p-type semiconductor.
Question 8
1 / -0

Different voltage are applied across a p-n junction and the currents are measured for each value. Which of the following graphs is obtained between voltage V and current i:

A

B

C

D

Solution

When different voltage are applied across a $$p-n$$ junction and the currents are measured then,
1. If $$p-n$$ junction is forward biased, then diode allow only a small electric current.However this small electric current is considered as negligible.
2. When the external voltage applied on the diode $$(Si)$$ diode reaches $$0.7V$$ the $$p-n$$ junction diode starts allowing large electric current through it.
3. At this point a small increase in voltage increases the electric current rapidly.
4. If $$p-n$$ junction is reversed ,biased very small number of minority charges carrier is present.Hence a small voltage applied on the diode pushes all the minority carrier towards the junction.Thus, further increase in the external voltage does not increases the electric current.
5. The electric current is called reverse saturation current and it remains constant with the increase in voltage.
6. However, if the voltage applied on the diode is increased continuously, the $$p-n$$ junction diode reaches to a state where junction breakdown occurs and reverse current increases rapidly.
Question 9
1 / -0

When an intrinsic semiconductor is connected to an electric cell, the holes move towards the _________ terminal of the cell.

A
Holes, negative positive

B
Electron, negative

C
Electrons, positive

D
Both (1) and (3)

Solution
Question 10
1 / -0

In an unbiased p-n junction, holes diffuse from the p-region to n-region because

A
Free electrons in the n-region attract them.

B
They move across the junction by the potential difference.

C
Hole concentration in p-region is more as compared to n-region.

D
All of the above.

Solution

The diffusion of charge carriers across a junction takes place from the region of higher concentration to the region of lower concentration. In this case, the p-region has greater concentration of holes than the n-region. Hence, in an unbiased p-n junction, holes diffuse from the p-region to the n-region.