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Electronics Fundamentals MCQs.net

Electronics Fundamentals MCQs.net

MCQs on Fundamentals of Electronics

Insulators are defined as materials that

Insulators are defined as materials that:

  1. Do not conduct electrical current under normal conditions
  2. Easily conduct electrical current
  3. Have electrical conduction properties in between conductors and insulators
  4. None of above

Correct answer: 1. Does not conduct electrical current under normal conditions

Explanation:

  • Insulators are defined as materials that don’t conduct electric current under normal conditions
  • Majority of good insulators are compounds rather than single-element materials
  • Insulators usually have very high resistivities
  • Valence electrons in insulators are tightly bound to the atoms
  • Very few free electrons are available in an insulator
  • Rubber, plastics, glass, mica, and quartz are a few examples of insulators

Conductors are defined as materials that

Conductors are defined as materials that:

  1. Do not conduct electrical current under normal conditions
  2. Easily conduct electrical current
  3. Have electrical conduction properties in between conductors and insulators
  4. None of above

Correct answer: 2. Easily conduct electrical current

Explanation:

  • Conductors are the materials that possess electrical conduction ability
  • Metals are good conductors of electricity
  • Among conductors, the best ones are single-element materials
  • Examples of good conductors include: Copper (Cu), Silver (Ag), Gold (Au), and aluminium (Al)
  • Good conductors are characterized by atoms with only one valence electron
  • In good electric conductors the valence electrons are very loosely bound to the atom. These loosely bound valence electrons become free electrons.
  • In a conductive material the free electrons are valence electrons.

Semiconductors are defined as materials that

Semiconductors are defined as materials that:

  1. Do not conduct electrical current under normal conditions
  2. Easily conduct electrical current
  3. Have electrical conduction properties in between conductors and insulators
  4. None of above

Correct answer: 3. Have electrical conduction properties in between conductors and insulators

Explanation:

  • Semiconductors are defined as materials that do not conduct electrical current under normal conditions
  • In the pure intrinsic state, a semiconductor is neither a good conductor nor a good insulator
  • Examples of single-element semiconductors include antimony (Sb), arsenic (As), astatine (At), boron (B), polonium (Po), tellurium (Te), silicon (Si), and germanium (Ge).
  • Examples of compound semiconductors include gallium arsenide, indium phosphide, gallium nitride, silicon carbide, and silicon germanium
  • Single-element semiconductors are characterized by atoms with four valence electrons
  • Of all semiconductors, silicon is the most commonly used

The most commonly used semiconductor is

The most commonly used semiconductor is:

  1. Carbon
  2. Silicon
  3. Sulphur
  4. Germanium

Correct answer: 2. Silicon

Explanation: Silicon is the most commonly used semiconductor that is widely employed in electronic devices and components around us. Silicon is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor.

  • Symbol: Si
  • Atomic number: 14
  • Atomic mass: 28.0855 u
  • Electron configuration: [Ne] 3s²3p²
  • Electrons per shell: 2, 8, 4
  • Melting point: 1,410 °C
  • Van der Waals radius: 210 pm

Semiconductor is formed by

Semiconductor is formed by:

  1. Co-ordinate bonds
  2. Covalent bonds
  3. Electrovalent bonds
  4. None of these

Correct answer: 2. Covalent bonds

Explanation:  A semiconductor is formed by Covalent bonds. A covalent bond consists of two atoms sharing a single electron.

Covalent bonding in Silicon

The outermost shell of atom can hold up to eight electrons. In case of silicon, the outermost orbit has only four electrons. In order to become most stable silicon atom needs four more electrons. Silicon atom forms four covalent bonds with four neighbouring atoms. In covalent bonding each valence electron is shared by two atoms. Whenever silicon atoms come in proximity to each other, each of the valence electron of atom is shared with neighbouring atom and each valence electron of a neighbouring atom is shared with this atom.

Number of valence electrons in pentavalent impurity are

Number of valence electrons in pentavalent impurity are:

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

Correct answer: 3. 5

Explanation: A pentavalent impurity atom has 5 valence electrons. Examples of pentavalent impurity atoms include Phosphorus (P), Arsenic (As), Antimony (Sb), etc.

As doping increases, bulk resistance of semiconductor

As doping increases, bulk resistance of semiconductor:

  1. Increases
  2. Decreases
  3. Remains the same
  4. None of these

Correct answer: 2. Decreases

Explanation: Doping is defined as the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties.

With an increase in doping, the conductivity also increases, this will increase the temperature inside.

Since temperature and resistance are inversely related to each other, the bulk resistance will decrease.

In depletion region of pn junction, there is shortage of

In depletion region of pn junction, there is shortage of:

  1. Acceptor ions
  2. Donor ions
  3. Holes and electrons
  4. None of these

Correct answer: 3. Holes and electrons

Explanation: The depletion region of a p-n junction is formed due to the shortage of holes and electrons.

Ratio of number of holes and free electrons in intrinsic semiconductor is

Ratio of number of holes and free electrons in intrinsic semiconductor is:

  1. Less than 1
  2. 1
  3. More than 1
  4. None of these

Correct answer: 2. 1

Explanation: The ratio of number of holes and free electrons in intrinsic semiconductor is 1.

Resistance of pure semiconductor on heating

Resistance of pure semiconductor on heating:

  1. Goes up
  2. Goes down
  3. Remains same
  4. None of these

Correct answer: 2. Goes down

Explanation: When pure semiconductor is heated, some of the covalent bonds in it break thus producing free electrons and holes. Due to generation of more charge carriers the conductivity increases and resistance decreases.

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