Free Physics of Solids MCQs with Answers

21. 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.

22. 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.

23. Which of the following substances possesses the highest elasticity?

• A. Rubber
• B. Steel
• C. Glass
• D. Copper

Explanation: Rubber possesses the highest elasticity among the given options. It can undergo significant deformation under stress and return to its original shape when the stress is removed. This property is due to the molecular structure of rubber, which allows its polymer chains to stretch and then recoil.

24. What is the SI unit of modulus of elasticity of a substance?

• A. Nm^-2
• B. Jm^-2
• C. Nm^-1
• D. Being a number, it has no unit

Explanation: The modulus of elasticity, also known as Young's modulus, measures the stiffness of a material. It is defined as the ratio of stress to strain within the elastic limit of the material. The SI unit of modulus of elasticity is Newton per square meter (Nm^-2) or Pascal (Pa). Therefore, option c) Nm^-1 is the correct SI unit for modulus of elasticity.

25. What are the dimensions of stress?

• A. MLT^-2
• B. ML^-2T^-1
• C. ML^-1T^-2
• D. ML^0T^-1

Explanation: Stress is defined as force per unit area and is expressed in units of pressure. The dimensional formula for pressure is force divided by area( p = F / A), which is MLT^-2 (mass × length × time^-2

26. Which one of the following physical quantities does not have the dimensions of force per unit area?

• A. Stress
• B. Strain
• C. Young modulus
• D. Pressure

Explanation: Explanation: Strain is a dimensionless quantity that represents the relative deformation or change in shape of a material due to stress. It is defined as the change in length per unit length and does not have the dimensions of force per unit area. Mathematically ε = Δ x/x,

27. If a wire is stretched to double of its length then the strain will be:

• A. zero
• B. 1
• C. 1/2
• D. double

Explanation: Strain is defined as the change in length per unit length. If a wire is stretched to double its original length, the strain will be the change in length divided by the original length, which is (2L - L) / L = 1. Therefore, the strain will be 1, or 100%. However, the options provided seem to have a typographical error as 1/2, which represents 50% strain, is the closest correct option.

28. A wire of length L is stretched by a length l when a force F is applied at one end. If the elastic limit is not exceeded, the amount of energy stored in the wire is

• A. Fl
• B. 1/2Fl
• C. Fl^2 /L
• D. 1/2fl^2

Explanation: The amount of energy stored in an elastic material when stretched is given by the formula 1/2 * force * extension. In this case, the force is F and the extension is l. Therefore, the energy stored in the wire is 1/2 * (F * l).

29. When a force is applied at one end of an elastic wire, it produces a strain e in the wire. If Y is the Young's modulus of the material of the wire, the amount of energy stored per unit volume of the wire is given by:

• A. Ye
• B. Ye²
• C. 1/2Ye
• D. 1/2Ye²

Explanation: The energy stored per unit volume in an elastic material is given by the formula 1/2 * stress * strain. In this case, stress is given by Young's modulus (Y) times strain (e). Therefore, the energy stored per unit volume is 1/2 * Y * e^2.

30. wire, suspended vertically from one end, is stretched by attaching a weight of 20 N to the lower end. The weight stretches the wire by 1 mm. How much energy is gained by the wire

• A. 0.01J
• B. 0.02J
• C. 0.04J
• D. 1J

Explanation: The energy gained by the wire is given by the formula 1/2 * force * extension. In this case, the force is 20 N and the extension is 0.001 m (1 mm = 0.001 m). Therefore, the energy gained by the wire is 1/2 * (20 N * 0.001 m) = 0.01 J.