Free Physics of Solids MCQs with Answers

41. Materials in which valence electrons are tightly bound to their atoms at low temperature are called

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

Explanation: Insulators have tightly bound valence electrons that do not contribute significantly to electrical conduction at low temperatures.

42. The modulus of elasticity of liquids is

• A. 1
• B. zero
• C. infinity
• D. none of these

Explanation: Liquids do not have a modulus of elasticity in the same way that solids do. The concept of modulus of elasticity applies to the deformation of solids under the application of stress, and it is not relevant to liquids.

43. The Young's modulus of a wire of length L and radius r is Y. If the length is reduced to L/2 and radius to r/2, its Young's modulus will be

• A. Y/2
• B. 2Y
• C. Y
• D. 4Y

Explanation: Young's modulus (Y) is a material property and does not depend on the dimensions of the specimen. Therefore, reducing the length and radius of the wire does not change its Young's modulus.

44. Which of the following is not true for a crystalline substance?

• A. short range order
• B. no definite melting point
• C. sharp melting point
• D. All

Explanation: Crystalline substances typically have a well-defined, sharp melting point. Therefore, the statement "No definite melting point" is not true for a crystalline substance.

45. A completely filled band is called:

• A. Conduction Band
• B. Valence Band
• C. Forbidden band
• D. Core band

Explanation: The valence band is completely filled with electrons, and these electrons are involved in chemical bonding

46. The electrons in the conduction band are free to:

• A. Transports vibration
• B. Transports signals
• C. Transports charge
• D. Transports impulses

Explanation: Electrons in the conduction band are free to move and carry an electric charge, contributing to electrical conductivity.

47. With an increase in temperature, the electrical conductivity of intrinsic semiconductors

• A. Decreases
• B. Increases
• C. Remain the same
• D. First increases then decreases

Explanation: In intrinsic semiconductors, increasing the temperature leads to more thermal generation of charge carriers (electrons and holes), which results in increased carrier concentration and, consequently, increased conductivity.

48. Holes can exist in

• A. Conductors
• B. Insulators
• C. Semiconductors
• D. All of the above

Explanation: Holes can exist in all types of materials: conductors, insulators, and semiconductors. In semiconductors, holes are essentially vacancies in the valence band that behave like positive charge carriers.

49. Young's modulus is a proportionality constant that relates the force per unit area applied perpendicularly at the surface of an object to

• A. the shear
• B. the fractional change in volume
• C. the fractional change in length
• D. the pressure

Explanation: Young's modulus (E) is a measure of the stiffness of a material and is defined as the ratio of stress to strain in the linear elastic region. It relates the force per unit area applied perpendicularly to the surface of an object to the fractional change in length along the direction of the applied force.

50. In a semiconductor, the charge carriers are:

• A. Holes only
• B. Electrons only
• C. Electrons and holes both
• D. None of these

Explanation: Semiconductors can have both electrons and holes as charge carriers. Electrons are the majority carriers in n-type semiconductors, while holes are the majority carriers in p-type semiconductors.