Free Physics of Solids MCQs with Answers

201. Materials having permeability largely greater than one are

• A. Diamagnetic
• B. Paramagnetic
• C. Ferromagnetic
• D. None of these

Explanation: The correct answer is Ferromagnetic. Ferromagnetic materials have a permeability that is significantly greater than one, which means they can be strongly magnetised. This is due to the alignment of their internal magnetic domains in response to an external magnetic field. In contrast, diamagnetic materials have a permeability less than or equal to one and are repelled by magnetic fields, while paramagnetic materials have a permeability slightly greater than one and are weakly attracted by magnetic fields. The option None of these is incorrect because ferromagnetic materials fit the description given in the question.

202. The substance which is repelled by or opposed by the applied magnetic field is

• A. Diamagnetic
• B. Paramagnetic
• C. Ferromagnetic
• D. All of these

Explanation: The correct answer is Diamagnetic. Diamagnetic substances are repelled by a magnetic field because they create an induced magnetic field in a direction opposite to that of the applied magnetic field. This is due to the paired electrons in the material that result in no net magnetic moment. In contrast, Paramagnetic substances are weakly attracted to magnetic fields due to the presence of unpaired electrons. Ferromagnetic substances are strongly attracted to magnetic fields and can become permanently magnetised. Therefore, the option 'All of these' is incorrect as it includes substances that are not repelled by a magnetic field.

203. The area of hysteresis loop is

• A. Magnetism
• B. Demagnetism
• C. Energy dissipation per cycle
• D. All of the above

Explanation: The area of the hysteresis loop represents the energy dissipated as heat due to internal friction during each cycle of magnetisation and demagnetisation. This phenomenon is tied to the resistive forces within the material. Magnetism and demagnetism are related concepts, but do not specifically describe the area of the hysteresis loop. 'All of the above' is incorrect because not all listed concepts are represented by the loop area.

204. Curie temperature is the temperature by which

• A. Ferromagnetic material changes to paramagnetic material
• B. Paramagnetic material changes to ferromagnetic material
• C. Diamagnetic material changes to ferromagnetic material
• D. Ferromagnetic material changes to diamagnetic material

Explanation: The Curie temperature is the threshold at which a ferromagnetic material becomes paramagnetic. This is because, at higher temperatures, thermal energy overcomes the magnetic energy that aligns the spins in a ferromagnetic material. Option A is correct because it accurately describes this transition. Option B is incorrect because paramagnetic materials do not spontaneously become ferromagnetic at the Curie temperature. Option C is incorrect because diamagnetic materials have no relation to ferromagnetic properties in this context. Option D is incorrect because ferromagnetic materials do not transition to diamagnetic materials at any temperature.

205. The resistance at critical temperature is

• A. Micro ohm
• B. Pico ohm
• C. Mega ohm
• D. Zero

Explanation: Superconductors are materials that, below a specific critical temperature, exhibit zero electrical resistance. This means that they can conduct electricity without any energy loss. When a material becomes superconducting, its resistance drops abruptly to zero. Therefore, the correct answer is zero resistance at the critical temperature. The other options (micro ohm, pico ohm, mega ohm) all represent some level of non-zero resistance, which does not occur in a superconducting state.

206. The resistivity range for semiconductors in ohm-meter is

• A. 10-2 to 102
• B. 10-6 to 101
• C. 106 to 108
• D. 10-8 to 108

Explanation: The correct answer is 10-6 to 101 ohm-meter, which is characteristic of semiconductors. Semiconductors have resistivity values that are between those of conductors (which have very low resistivity) and insulators (which have very high resistivity). Option A is incorrect because it suggests a range typical of conductive materials. Option C is incorrect because it represents the range of insulating materials. Option D is incorrect because it encompasses a wide range, including values for conductors, semiconductors, and insulators, which does not accurately represent semiconductors specifically.

207. A valence band is

• A. Hole donor
• B. Electron donor
• C. Electron acceptor
• D. All of these

Explanation: The valence band in a solid is the energy band that is filled with electrons at absolute zero temperature. It can act as an electron donor when electrons gain enough energy to jump to the conduction band, enabling electrical conductivity. Option B is correct because the valence band effectively donates electrons to the conduction band. Option A is incorrect because the valence band is not primarily a hole donor, although the absence of electrons can create 'holes.' Option C is incorrect because the valence band does not accept electrons; it is initially filled with them. Option D is incorrect because not all provided options correctly describe the role of a valence band.

208. Which one of the following statement is wrong?

• A. Young's modulus for a perfectly rigid body is zero
• B. Bulk modulus is relevant for solids, liquids, and gases
• C. Rubber is less elastic than steel
• D. The Young's modulus and shear modulus are relevant for solids

Explanation: The correct answer is Option A: 'Young's modulus for a perfectly rigid body is zero' because it is incorrect. A perfectly rigid body would have an infinite Young's modulus since it would not deform under any amount of applied stress, indicating infinite resistance to deformation. Option B is correct because the bulk modulus is applicable to solids, liquids, and gases, describing their responses to uniform compression. Option C is correct because, in terms of physics, steel is more elastic than rubber, meaning it returns to its original shape better after stress. Option D is correct because Young's modulus and shear modulus are indeed relevant for describing the mechanical behaviour of solids.

209. What will be energy stored in a strained wire?

• A. 1/2 × Load × Extension
• B. 1/2 × Stress × Strain
• C. 1/2 × Load × Strain
• D. 1/2 × Load × Stress

Explanation: The energy stored in a strained wire is given by the formula 1/2 × Load × Extension. This formula is derived from the work done on the wire, which is the integral of force over distance. Option A correctly represents this relationship. In contrast, Option B represents the energy density, which is suitable for understanding the energy per unit volume within the material, not the total energy stored. Options C and D incorrectly relate the variables, as they fail to incorporate the correct physical relationships necessary for calculating the total energy stored in the wire.

210. The maximum load a wire can withstand without breaking, when its length is reduced to half of its original length will

• A. Double
• B. Be halved
• C. Four times
• D. Remains the same

Explanation: The ability of a wire to withstand a load without breaking is related to its cross-sectional area and its length. By halving the length of the wire, its cross-sectional area effectively doubles, assuming volume remains constant. This increase in cross-sectional area allows the wire to withstand a greater load, specifically double the original. Thus, the maximum load it can withstand doubles. Options B, C, and D are incorrect because they do not accurately describe the relationship between the length and load-bearing capacity of the wire.