Free Electrical Properties of Solids MCQs with Answers

11. The substance(s) in which the atoms do NOT form magnetic dipole is/ are calledI. ferromagneticII. paramagneticIII. diamagnetic

• A. I only.
• B. III only.
• C. I and II.
• D. II and III.

Explanation: Diamagnetic substances are those in which the atoms do not possess a permanent magnetic dipole moment. When an external magnetic field is applied, a magnetic dipole moment is induced in the opposite direction of the applied field.

12. In terms of energy band, semiconductor materials at room temperature do NOT have

• A. partially filled valence band.
• B. partially filled conduction band
• C. plenty of free electrons for electrical conduction
• D. narrow forbidden energy gap between conduction and valence band

Explanation: Semiconductor materials at room temperature do not have a partially filled conduction band, as this would indicate metallic behavior. The correct answer is that they have a partially filled valence band, which is essential for their conductivity. The other options are incorrect because semiconductor materials do not have a narrow forbidden energy gap like insulators, nor do they have plenty of free electrons like metals.

13. Conductivity of a semiconductor material increases byI. increasing temperature.II. increasing the surface area.III. decreasing the density of charge carriers.IV. doping with small amounts of impurities.

• A. I and III.
• B. I and IV.
• C. II and III.
• D. II and IV.

Explanation: The correct answer is Option B: I and IV. Conductivity in semiconductors increases with temperature because thermal energy excites more electrons into the conduction band, thus increasing the number of charge carriers. Doping with small amounts of impurities introduces additional charge carriers (electrons or holes), which enhances conductivity.Option A is incorrect because although increasing temperature increases conductivity, decreasing the density of charge carriers would reduce conductivity. Option C is incorrect as increasing surface area does not directly affect conductivity, and decreasing the density of charge carriers would reduce it. Option D is incorrect because increasing surface area does not directly enhance conductivity, even though doping does.

14. Which of the following materials has the maximum energy gap?

• A. Insulator
• B. Conductor
• C. Semiconductor
• D. Superconductor

Explanation: The correct answer is Insulator. Insulators have the largest energy gap among the given options, which prevents electrons from easily transitioning to the conduction band, thus inhibiting electrical conductivity. In contrast, conductors have either overlapping bands or very small energy gaps, allowing electrons to move freely. Semiconductors have a smaller energy gap than insulators, which can be overcome under certain conditions. Superconductors, when in their superconducting state, have negligible energy gaps, allowing for resistance-free electron flow.

15. Which types of impurity is added to a semiconductor material so that it can provide holes?

• A. Trivalent
• B. Tetravalent
• C. Pentavalent
• D. Monovalent

Explanation: The correct answer is Trivalent. Trivalent impurities, such as Boron, have three valence electrons. When added to a semiconductor material, they create 'holes' by accepting electrons, leading to the formation of a p-type semiconductor, which is characterized by the presence of holes as majority carriers.Other options are incorrect because tetravalent impurities do not alter the balance of electrons and holes in the semiconductor. Pentavalent impurities add extra electrons rather than creating holes, resulting in an n-type semiconductor. Monovalent impurities are not suitable for semiconductor doping to create holes or electrons.

16. Dark plastic handlers often used on kitchen utensils because:

• A. The black material is good in radiation.
• B. The plastic is good insulator.
• C. The plastic is a good conductor.
• D. The plastic soften gradually with excessive heat.

Explanation: Cooking pots are provided with wooden or plastic handles because they are bad conductors of heat. This prevents the heat from the pan to transfer to our hands.

17. Ferromagnetic means:

• A. It is attracted by magnet
• B. It is iron-like in nature
• C. It can be magnetized
• D. It is an alkali metal

Explanation: The explanation for this question will be added soon.

18. The electrical conductivity of metal sometimes decreases with the?

• A. Increase in pressure
• B. Increase in temperature
• C. Decrease in temperature
• D. Decrease in pressure

Explanation: The electrical conductivity of metals decreases with an increase in temperature as with the increase in temperature, the positive metal ions also begin to oscillate and the motion hinders the free movement of mobile electrons between the positive ions.This hindrance decreases the electrical conductivity.

19. Which one of them can conduct electricity in solid state?

• A. Diamond
• B. Graphite
• C. Nail
• D. Iodine

Explanation: Graphite, C(s) can conduct electricity in a solid state. Graphite is a network solid and conducts electricity as it has delocalized molecular orbitals in which delocalized electrons are free to move. Hence, option B is correct.