Free Physics of Solids MCQs with Answers

61. Energy bands in solids which are either partially filled or empty are called

• A. valence band
• B. forbidden band
• C. conduction band
• D. innermost band

Explanation: In solid-state physics, the energy bands in solids are categorized into the valence band, conduction band, and forbidden band (also known as band gap). The conduction band is the energy band where electrons can move freely, conducting electricity. It is partially filled or empty depending on the number of available electrons in the material

62. After Curie temperature, iron becomes

• A. ferromagnetic
• B. paramagnetic
• C. diamagnetic
• D. superconductor

Explanation: After the Curie temperature, iron loses its ferromagnetic properties and becomes paramagnetic. Above the Curie temperature, the thermal energy overcomes the magnetic ordering, and the material loses its net magnetic moment

63. Minimum number of atoms arranged in a solid showing the whole characteristics of the solid is called

• A. crystal
• B. unit cell
• C. molecules
• D. all are correct

Explanation: The minimum number of atoms arranged in a solid showing the whole characteristics of the solid is called a unit cell. A unit cell is the smallest repeating unit in a crystal lattice that retains the symmetry and characteristics of the entire crystal structure

64. Superconductors with a critical temperature above 77 K are called

• A. low temp superconductor
• B. high temp superconductor
• C. superconductors do not exist above 77 K
• D. moderate temp superconductor

Explanation: Superconductors with critical temperatures above 77 K are categorized as high-temperature superconductors. These materials can undergo superconductivity at temperatures higher than the boiling point of liquid nitrogen (77 K). Examples include certain ceramic materials like yttrium barium copper oxide (YBCO) and bismuth strontium calcium copper oxide (BSCCO)

65. In an atom, the magnetic field exists due to

• A. orbital motion of electron
• B. spinning of proton
• C. spinning of electron
• D. all

Explanation: In an atom, the magnetic field exists due to various phenomena:The orbital motion of electrons generates a magnetic field.The spinning of electrons (electron spin) also produces a magnetic field.The spinning of protons contributes to the overall magnetic field of the atom. Thus, the magnetic field in an atom arises from the combined effects of electron orbital motion, electron spin, and proton spin.

66. The SI unit of Stefan's constant is

• A. Wm⁻²K²
• B. Wm²K⁻⁴
• C. Wm⁻⁴K⁴
• D. Wm⁻⁴K⁻⁴

Explanation: tefan's constant (σ) is expressed in the SI unit of Wm2K−4Wm2K−4.Incorrect Options and Explanations: (a) Wm⁻²K² - This unit does not represent Stefan's constant. (c) Wm⁻⁴K⁴ - This unit does not represent Stefan's constant. (d) Wm⁻⁴K⁻⁴ - This unit does not represent Stefan's constant.

67. The ratio of volumetric strain to volumetric stress is called

• A. Compressibility
• B. Young's modulus
• C. Bulk's modulus
• D. Shear's modulus

Explanation: The ratio of volumetric strain to volumetric stress is called c. Bulk's modulus.Here's why:Volumetric strain: It represents the relative change in volume of a material due to applied pressure. It is calculated as the change in volume divided by the original volume.Volumetric stress: It represents the pressure applied to a material, which causes a change in its volume.Bulk modulus (B) is defined as the ratio of volumetric stress (ΔP) to the volumetric strain (ΔV/V):B = ΔP / (ΔV/V)Therefore, Bulk's modulus is the material property that relates the relative change in volume to the applied pressure, making it the correct answer among the options.Young's modulus: It measures the stiffness of a material under tensile or compressive stress (along a single axis), not volumetric stress.Shear modulus: It measures the resistance of a material to deformation under shearing forces, not volumetric stress.Compressibility: This is the reciprocal of Bulk's modulus, not the ratio itself.

68. A block weighing 40 kg extends a spring by 0.16m from its unscratched position. What is the value of k?

• A. 170 kg/s2
• B. 245 kg/s2
• C. 215 kg/s2
• D. 201 kg/s

Explanation: Hooke's Law describes the relationship between the force exerted by a spring (F) and its displacement (x) from the equilibrium position. The formula is given by:F=−kxWhere F is the force exerted by the spring,k is the spring constant,x is the displacement from the equilibrium position.The negative sign indicates that the force exerted by the spring is in the opposite direction to the displacement.Given that the block weighs 40kg and the spring is extended by 0.16m, the force exerted by the spring (F) can be calculated using the weight (W=mg), where m is the mass and g is the acceleration due to gravity:F= mgmg=-kxk= -2450N/mSince the spring constant (k) is a positive value (magnitude), the answer is:k= 2450 N/m

69. The length of a spring is α when a force of 4 N is applied on it the length is β when 5 N forces is applied then the length of spring when 9N force is applied is:

• A. 5β - 4α
• B. β - α
• C. 5α -4β
• D. 9(β - α)

Explanation: The relationship between the force applied on a spring and the resulting displacement can be described by Hooke's Law, which states that the force (F) exerted on a spring is directly proportional to the displacement (x) from its equilibrium position. Mathematically, this can be expressed as:F=−kxwhere k is the spring constant.In this case, the force (F) is related to the change in length (Δx) of the spring, and we can write:F=kΔxThe change in length (Δx) is given by β−α.The correct option is:9(β - α)

70. Crystalline solids have the properties such as

• A. Regular arrangement
• B. Covalent arrangement
• C. Somewhat defective
• D. All of them

Explanation: Crystalline solids have a regular and repeating arrangement of atoms or molecules, giving them characteristic geometric shapes.