Electronic Science (Test 5)

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Electronic Science

Electronic Science
| Electric Circuits | | Electrical and Electronic Measurements | | Power Electronics | | Electronic Devices | | Analog Circuits | | Digital Circuits | | Digital Logic | | Electrostatic Potential and Capacitance | | Current Electricity | | Moving Charges and Magnetism | | Magnetism and Matter | | Electronic Devices |
Q.1
In a pure, or intrinsic, semiconductor, valence band holes and conduction-band electrons are always present
A. in equal numbers
B. such that number of electrons is greater than the number of holes
C. such that number of holes is greater than the number of electrons
D. None of these
Answer : Option A
Explaination / Solution:

An intrinsic semiconductor, also called an undoped semiconductor or i-type semiconductor, is a pure semiconductor without any significant dopant species present. The number of charge carriers is therefore determined by the properties of the material itself instead of the amount of impurities. In intrinsic semiconductors the number of excited electrons and the number of holes are equal: n = p.

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Q.2
Diffusion in a p-n junction is due to
A. concentration gradient
B. minority carriers
C. carrier injection
D. None of these
Answer : Option A
Explaination / Solution:

  • In n-type semiconductor, the concentration of electrons is more compared to the concentration of holes. Similarly, in p-type semiconductor, the concentration of holes is more compared to the concentration of electrons
  • The first process that occurs in the p-n semiconductor is diffusion
  • In the formation of the p-n junction, due to the concentration gradient across the p and the n sides, the electrons diffuse from n region to p region and the holes diffuse from p region to n region.

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Q.3
The impurity atoms with which pure silicon should be doped to make a p-type semiconductor are those of
A. Boron
B. Bismuth
C. Phosphorus
D. Antimony
Answer : Option A
Explaination / Solution:

In a pure (intrinsic) Si or Ge semiconductor, each nucleus uses its four valence electrons to form four covalent bonds with its neighbors . Each ionic core, consisting of the nucleus and non-valent electrons, has a net charge of +4, and is surrounded by 4 valence electrons. Since there are no excess electrons or holes In this case, the number of electrons and holes present at any given time will always be equal. Note each +4 ion is surrounded by four electrons. Now, if one of the atoms in the semiconductor lattice is replaced by an element with three valence electrons, such as a Group 3 element like Boron (B) or Gallium (Ga), the electron-hole balance will be changed. This impurity will only be able to contribute three valence electrons to the lattice, therefore leaving one excess hole . Since holes will "accept" free electrons, a Group 3 impurity is also called an acceptor. A semiconductor doped with an acceptor. An excess hole is now present. Because an acceptor donates excess holes, which are considered to be positively charged, a semiconductor that has been doped with an acceptor is called a p-type semiconductor.

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Q.4
A solid having uppermost energy – band partially filled with electrons is called
A. none of the above
B. a semi – conductor
C. an insulator
D. a conductor
Answer : Option D
Explaination / Solution:
No Explaination.


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Q.5
Transistor was invented by
A. Lee de Forest
B. Marconi
C. Shockley
D. Fleming
Answer : Option C
Explaination / Solution:

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit. The first practically implemented device was a point-contact transistor invented in 1947 by American physicists John Bardeen, Walter Brattain, and William Shockley. The transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The transistor is on the list of IEEE milestones in electronics, and Bardeen, Brattain, and Shockley shared the 1956 Nobel Prize in Physics for their achievement.

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Q.6
In which case of comparing solenoid and bar magnet there is no exact similarity?
A. moving a small compass needle in the neighbourhood of a solenoid enables tracing the flux lines
B. There is a current entering and a current leaving a solenoid
C. soenoid can be broken into two weaker solenoids
D. flux lines enter one end of a solenoid
Answer : Option B
Explaination / Solution:
No Explaination.


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Q.7
if   =magnetic intensity,  =susceptibility, magnetic moment per unit volume     equals

A. μ0μr
B. μ00.8μr
C. μ01.2μr
D. μ01.5μr
Answer : Option A
Explaination / Solution:
No Explaination.


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Q.8
To increase the magnetic field of a solenoid what core material should be used ?
A. Ferromagnetic material
B. diamagnetic material
C. Ferrimagnetic material
D. paramagnetic material
Answer : Option A
Explaination / Solution:
No Explaination.


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Q.9
If a magnet is suspended over a container of liquid air, it attracts droplets to its poles. The droplets contain only liquid oxygen and no nitrogen because
A. oxygen is ferromagnetic whereas nitrogen is diamagnetic
B. oxygen is diamagnetic whereas nitrogen is paramagnetic
C. oxygen is ferrimagnetic whereas nitrogen is diamagnetic
D. oxygen is paramagnetic whereas nitrogen is diamagnetic
Answer : Option D
Explaination / Solution:
No Explaination.


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Q.10
A bar magnet of magnetic moment 1.5 J/T lies aligned with the direction of a uniform magnetic field of 0.22 T. What is the amount of work required by an external torque to turn the magnet so as to align its magnetic moment opposite to the field direction?
A. 0.86J
B. 0.76J nC
C. 0.56J
D. 0.66J
Answer : Option D
Explaination / Solution:
No Explaination.


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