Free Physics of Solids MCQs with Answers

101. The energy band gap in semiconductor is:

• A. Zero
• B. Very high
• C. Narrow
• D. Infinite

Explanation: Semiconductors have a narrow but non-zero energy band gap(typically between 0.2 eV and 3 eV).This allows them to act as insulators at absolute zero but conduct electricity when thermal or electrical energy is applied.

102. Domain formation is the necessary feature of:

• A. Ferromagnetism
• B. Paramagnetism
• C. Diamagnetism
• D. All of these

Explanation: Ferromagnetism is characterized by the presence ofmagnetic domains, which are microscopic regions where themagnetic moments of atoms are aligned. The alignment ofthese domains in an external field is what causes the strong magnetic properties of these materials.

103. Longitudinal strain is possible in:

• A. Gases
• B. Liquids
• C. Solids
• D. All of these

Explanation: Longitudinal strain (change in length per unit length)requires a material to have a definite shape to resist tensileor compressive forces. Only solids possess this property,while liquids and gases will flow.

104. Shear modulus is zero for:

• A. Solids
• B. Liquids
• C. Gases
• D. Liquids and gases

Explanation: The shear modulus measures resistance to a change inshape without a change in volume. Since both liquids andgases lack a definite shape and flow when a shear force isapplied, they cannot resist shear stress, giving them a shearmodulus of zero.

105. Curie temperature of iron is the temperature below which it is:

• A. Diamagnetic
• B. Ferromagnetic
• C. Low retentivity
• D. Both (a) and (c)

Explanation: The Curie temperature is a critical point for magneticmaterials. Below this temperature, a material like ironexhibits strong ferromagnetic properties; above it, thermalagitation overcomes the magnetic alignment, and itbecomes paramagnetic.

106. A diamagnetic material in a magnetic material moves:

• A. From stronger to the weaker parts of the field
• B. From weaker to the stronger parts of the field
• C. Perpendicular to the field
• D. In none of the above directions

Explanation: Diamagnetic materials are weakly repelled by magneticfields. As a result, when placed in a non-uniform magneticfield, they will experience a net force pushing them from theregion of higher field strength to the region of lower fieldstrength.

107. For the formation of permanent magnets, the material should have

• A. High coercivity
• B. Low coercivity
• C. Low retentivity
• D. Both (a) and (c)

Explanation: A permanent magnet must be able to resist demagnetizationfrom external fields. This property is called coercivity, and ahigh coercivity is essential for a magnet to maintain itsmagnetism over time.

108. Core of the transformer is made up of

• A. Soft iron
• B. Steel
• C. Iron
• D. Alnico

Explanation: Transformer cores require a material that can be easilymagnetized and demagnetized with low energy loss. Softiron is used because it has high magnetic permeability andlow coercivity, minimizing hysteresis losses during the ACcycle.

109. A permanent magnet has the properties of retentivity and coercivity, which in magnitude are respectively

• A. High-high
• B. Low-low
• C. Low-high
• D. High-low

Explanation: To be a strong and lasting magnet, a material must havehigh retentivity (to retain a strong magnetic field) and highcoercivity (to resist being demagnetized by external fields ortemperature changes).

110. Electromagnets are made up of soft iron because soft iron has:

• A. Low retentivity and high coercive force
• B. High retentivity and high coercive force
• C. Low retentivity and low coercive force
• D. High retentivity and low coercive force

Explanation: Electromagnets need to be switched on and off easily. Softiron is ideal because it has low retentivity (it doesn't staymagnetized) and low coercivity (it's easy to magnetize anddemagnetize), allowing for rapid control of the magnetic field.