Free Physics of Solids MCQs with Answers

121. The process of adding controlled impurities to a semiconductor is known as _. The amount of impurity added to an intrinsic (pure) semiconductor varies its level of conductivity.

• A. Crystallography
• B. Rectification
• C. Intrinsic defects
• D. Doping

Explanation: Doping. The conductivity of semiconductors may easily be modified by introducing impurities into their crystal lattice.

122. When applied stress changes the volume, the change in volume per unit volume is known as:

• A. Polymetric strain
• B. Crystalline strain
• C. Volumetric strain
• D. Equal strain

Explanation: The change in volume per unit volume is known as volumetric strain. It is a measure of how much the volume of a material changes in response to an applied stress. The volumetric strain is calculated as the change in volume divided by the original volume.

123. The product of dimensions of Young's modulus and stress are:

• A. [ML2T-1]
• B. [ML-1T2]
• C. [ML-1T-2]
• D. [ML2T-3]

Explanation: The formula for Young's Modulus is:Where E is Young's Modulus/pressureσ is stress/ force per unit areaΜ is strain/ proportional deformationIf you observe the formula, strain is the ratio of the same dimensions. Hence, strain is a dimensionless quantity.Therefore, Young's modulus has the same dimensions that stress has.[ML−1T−2]

124. Which material will follow the below stress-strain curve?

• A. Copper
• B. Iron
• C. Lead
• D. Glass

Explanation: A stress-strain curve is a graphical way to show the reaction of a material when a load is applied. It shows a comparison between stress and strain.Brittle materials, which comprise cast iron, glass, and stone, are characterized by the fact that rupture occurs without any noticeable prior change in the rate of elongation. Thus, for brittle materials, there is no difference between the ultimate strength and the breaking strength.

125. Which of the following can have a negative temperature coefficient?

• A. Compounds of silver
• B. Liquid metals
• C. Metallic alloys
• D. Electrolytes

Explanation: All metals and alloys of metals show a positive temperature coefficient. Electrolytes can have negative temperature coefficient. Thus, option D is correct.

126. One of the following is a photoconductor :

• A. Silver
• B. Gold
• C. Selenium
• D. Mercury

Explanation: Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation. The photoconductivity of grey selenium arises from the ability of incident light to excite electron across its reasonably small band gap (2.6 eV in the crystalline form, 1.8 eV in the amorphous form).

127. Strain energy in deformed energy is stored in the form of:

• A. Elastic Energy
• B. Potential Energy
• C. Plastic Energy
• D. Kinetic Energy

Explanation: For an object that is deformed energy as stored as the potential energy and is known as the Strain energy.Elastic energy is the energy stored in a deformed object when it undergoes elastic deformation. This energy is stored in the form of potential energy within the object's molecular or atomic bonds.Potential energy is a type of energy associated with the position or configuration of an object. In the case of a deforming train, potential energy is stored as the train's shape changes. This potential energy can be released or converted into other forms of energy, such as kinetic energy, when the train returns to its original shape or undergoes further deformation.Plastic energy Is not a correct term.Kinetic energy is the energy of motion. While a deforming train may have some kinetic energy due to its motion.

128. A wire of area of cross-section 'A' and original length 'l' is subjected to a load 'L'. A second wire of the same material with an area is '2A' and a length of '2l' is subjected to the same load 'L'. If the extension in the first wire is 'X' and the second wire is 'Y', find the ratio 'X/Y'.

• A. 1:4
• B. 1:2
• C. 1:1
• D. 2:1

Explanation: To determine the correct ratio, we can use the formula for the extension of a wire under an applied load, which is given by Hooke's Law:Extension (ΔL) = (Load (L) * Length (l)) / (Area of Cross Section (A) * Young's Modulus (E))For the first wire: X = (L * l) / (A * E)For the second wire: Y = (L * 2l) / (2A * E)By simplifying the expressions, we find that X = Y, which means the extension in the first wire is equal to the extension in the second wire. Therefore, the correct ratio is 1:1.Hence, the correct option is c) 1:1, which represents the ratio of X/Y as 1:1.

129. The ratio of tensile stress to tensile strain is called:

• A. Modulus of elasticity
• B. Bulk Modulus
• C. Young's Modulus
• D. Shear Modulus

Explanation: Young's modulus is a measure of the stiffness of a material. It is defined as the ratio of tensile stress to tensile strain within the elastic limit of a material. In other words, Young's modulus is the ratio of the applied stress to the resulting strain, within the elastic limit of the material.Young's modulus is denoted by the symbol "E" and has the unit of Pascals (Pa) or Newtons per square meter (N/m²). It is a measure of how much a material will stretch (i.e. its elongation) under a given load. The higher the value of Young's modulus, the stiffer the material is.

130. A wire is stretched by a force 'F' which causes an extension ∆l, the energy stored in the wire is:

• A. F∆l
• B. 2F∆l
• C. ½ F∆l2
• D. ½ F∆l

Explanation: Given that, force applied = F . extension = ∆l and we assume the length of the wire to be = L.If the elastic limit is not exceeded then the stress is directly proportional to strain.Where stress is the amount of force applied per unit area (σ = F/A)And strain is extension per unit length (ε = ∆l/l)Hence,Energy stored = ½ x stress x strain x volumeEnergy stored = ½ x (F/A) x (∆l / L) x A x LEnergy stored = ½ F∆l