Physics Spl

Energy bands refer to how electrons behave in solids. In the case of conductors where the conductivity is high, the valence band and conduction band overlap which lets the electrons move freely. In the case of semiconductors, the valence and conduction bands have a small energy gap between them such as ?1 eV. There is a requirement for some external energy for electrons to jump to the conduction band. The gap is large in the case of insulators (>3 eV), making the electron movement nearly impossible. The energy band model differentiates how easily a material can conduct electricity. In semiconductors, there is controlled conductivity which is important for electronic devices as in these cases light or thermal energy can excite electrons.

According to the NCERT Solutions for Class 12 Physics Chapter 14 Semiconductor Electronics, intrinsic semiconductors are pure forms of semiconductor materials with no impurities like germanium or silicon. At room temperature, their conductivity is very low because they are solely based on thermally generated charge carriers (electrons and holes). On the other hand, extrinsic semiconductors to increase the conductivity, they are doped with impurities. P-type are doped with trivalent atoms (extra holes) and N-type semiconductors are doped with pentavalent atoms (extra electrons).
Doping makes extrinsic semiconductors far more conductive by enhancing the number of charge carriers. It becomes more practical for electronic devices like transistors, diodes, and integrated circuits.

Poisson's Ratio (? ) is used when a material is subjected to axial stress. It is the ratio of lateral strain to longitudinal strain. Mathematically, it is:

Derivation of the Poisson Ratio includes when a material is stretched, its width decreases (called lateral strain) and its length increases which is called longitudinal strain.

Poisson's Ratio (? ) is a dimensionless quantity and it is normally between a range of 0 to 0.5 for most materials. It is used in engineering applications including for bridge and building design. It is used in analyzing the structural deformations. Materials like rubber which has a high Poisson's ratio when stretched, exhibit significant lateral expansion.

According to the NCERT Solutions for Class 11 Physics Chapter 8 Mechanical Properties of Solids, when an external force is applied to a solid, the solid undergoes changes in shape or size which is called deformation. The solid deformation can be classified into:

Elastic Deformation: It is when the body returns to its original size and shape after the force is removed. It occurs within the elastic limit and follows Hooke's law. The most common examples include stretching a helical spring or a rubber band.

Plastic Deformation: It occurs beyond the elastic limit and here after the removal of the force, the body does not return to its original shape and size. Hence, the force applied leads to the permanent deformation of the solid. Common examples include deformation in putty, clay or bending of a metal wire beyond a certain limit.

The plastic deformation is irreversible and elastic deformation is reversible. These concepts are important when studying engineering, material science, and construction.

The modulus of elasticity refers to the material's capacity to withstand or resist deformation when stress is applied. There are three types of the modulus of elasticity including:

Young's Modulus (E): It is used to measure a solid's elasticity when longitudinal stress (tensile or compressive) is applied to it. Mathematically, it is represented by the following formula;

SI Unit is N/m² (Pascal, Pa).

Bulk Modulus (K): It is used to measure the ability of the material to resist volume change when uniform pressure is applied to it. Mathematically, it is:

SI Unit is N/m² (Pa)

Shear Modulus (G) or Modulus of Rigidity: It is used when a shear force is applied to measure the resistance to shape change. Mathematically, it is represented by:

SI Unit: N/m² (Pa)

The value of each modulus varies for different materials, and it describes different types of deformation.