Free Physics of Solids MCQs with Answers

181. Which one of the following are polymers?

• A. PVC
• B. Plastics
• C. Paints
• D. All of these

Explanation: The correct answer is that all of the options listed are linked to polymers. PVC is a specific type of polymer, commonly used in pipes and flooring due to its robustness. Plastics are materials made from polymer chains, known for their flexibility and wide range of uses. Paints contain polymer-based binders that help create a protective film on surfaces. Thus, all the listed options include polymers in their composition or structure, making 'All of these' the correct choice.

182. The number of atoms per unit cell of simple cubic is/are

• A. One
• B. Four
• C. Eight
• D. Six

Explanation: In a simple cubic unit cell, atoms are positioned at each of the eight corners of the cube. Each corner atom is shared among eight adjacent unit cells. Therefore, the contribution of each corner atom to the unit cell is 1/8th of an atom. With eight corners, the total number of atoms per unit cell is calculated as 8 * (1/8) = 1. This is why Option A is correct. Options B, C, and D suggest incorrect numbers of atoms based on different assumptions about the structure and sharing of atoms, which are not applicable to a simple cubic unit cell.

183. The number of atoms per unit cell in BCC are

• A. Two
• B. Four
• C. Six
• D. Nine

Explanation: In a body-centred cubic (BCC) unit cell, there is one atom located at the centre of the cell and eight atoms at the corners of the cube. Each corner atom is shared among eight adjacent unit cells. Therefore, each corner atom contributes 1/8th of an atom to the unit cell, and with eight corners, this adds up to 1 atom. Adding the single atom at the centre, there are a total of 2 atoms per unit cell. Option A is correct. Options B, C, and D are incorrect as they either correspond to other structures (like FCC for option B) or do not align with the BCC atomic distribution.

184. The size of one grain in polymers are

• A. 3Å to 4Å
• B. 2Å to 4Å
• C. 4Å to 7Å
• D. 5Å to 8Å

Explanation: In polymers, the crystalline regions, or grains, have a very compact structure due to the orderly arrangement of polymer chains. The typical size of these grains is between 3Å to 4Å. Option A correctly identifies this range. Options B, C, and D either extend beyond or below this range, making them incorrect as they do not accurately reflect the compact nature of polymer grains.

185. Tensile strain is the change in

• A. Length
• B. Area
• C. Volume
• D. All of these

Explanation: Tensile strain is defined as the ratio of the change in length of a material to its original length when subjected to a tensile force. This means it specifically measures the deformation along the length of the object. Option A is correct because tensile strain directly concerns this change in length. Options B and C are incorrect because they refer to changes in area and volume, respectively, which are not directly related to tensile strain. Option D is incorrect because tensile strain is not concerned with all dimensions but only with the length.

186. Shear strain is equal to

• A. Δx/L
• B. ΔL/L
• C. ΔL/x
• D. Angular deformation

Explanation: Shear strain is a measure of how much a material deforms under shear stress, typically defined by the angle change (angular deformation) in radians. In other words, it is the tangent of the angle of deformation due to applied shear forces. The incorrect options relate to the definitions of linear or normal strain (Δx/L and ΔL/L) or do not apply to standard strain measurements at all (ΔL/x).

187. Two dimensional modulus of elasticity is given by

• A. Y/σ
• B. Y/σ²
• C. Y/σ¹
• D. All of the above options are correct

Explanation: The correct expression for the two-dimensional modulus of elasticity is Y/σ², where Y is the Young's modulus and σ represents stress. This expression accounts for the squared relationship of stress in two-dimensional scenarios. Option A Y/σ and Option C Y/σ¹ imply incorrect relationships, while Option D All options are correct is incorrect, as it suggests multiple correct answers, which is not the case.

188. The ratio of bulk strain to bulk stress is called

• A. Young's modulus
• B. Bulk modulus
• C. 3D
• D. Compressibility

Explanation: The correct answer is Compressibility. Compressibility is defined as the reciprocal of the bulk modulus, which means it is the ratio of bulk strain to bulk stress. In contrast, the bulk modulus is the ratio of bulk stress to bulk strain, and Young's modulus pertains to tensile stress and strain. '3D' is not applicable to this context.

189. Bulk strain is

• A. 1D
• B. 2D
• C. 3D
• D. All options are correct

Explanation: Bulk strain, also known as volumetric strain, refers to the change in volume of a material when subjected to uniform pressure in all directions. This is a three-dimensional change, making it appropriate to classify it as 3D strain. Option C is correct because it accurately describes the nature of bulk strain. Option A is incorrect because 1D strain does not involve volume change, only elongation or compression along a single axis. Option B is incorrect because 2D strain refers to changes within a plane and does not account for the volume change in three dimensions. Option D is incorrect because bulk strain is specifically a 3D phenomenon, not applicable to all dimensions.

190. Choose the correct option for tensile strain.

• A. e < 0
• B. 0 < e < 1
• C. e > 1
• D. e = 1

Explanation: Tensile strain is defined as the change in length divided by the original length of an object. It is a dimensionless quantity that typically falls between 0 and 1 for most practical applications, indicating elongation without exceeding the original length significantly. Option B is correct because it accurately represents the usual range of tensile strain in materials that are not undergoing extreme deformation. Options A and D suggest incorrect values or conditions for tensile strain, while Option C suggests a strain greater than 1, which would imply very significant elongation not typical in most scenarios.