Physics Vidyapith ✍️

Prism Spectra 1.) Prism spectra are obtained by the phenomena of dispersion of light. 2.) Prism spectra have only one order. 3.) A prism spectrum is of bright intensity. 4.) In prism spectra, spectral colors overlap each other. 5.) Red color is dispersed least whereas violet color disperses the maximum. 6.) Prism spectrum depends upon the material of prism. 7.) The prism spectral lines are curved. . Grating Spectra 1.) Grating spectra are obtained by the phenomena of diffraction of light. 2.) Grating spectra has more than one order. 3.) Grating spectra is of less intensity. 4.) In grating spectra, there is no overlapping of color. 5.) Red color diffracts the maximum whereas violet color diffracts the least. 6.) Grating spectra are independent of the material of grating. 7.) The grating spectral lines are almost straight.

Interference 1.) It is due to the superposition of two or more than two wavefronts coming from coherent sources. 2.) The intensity of all bright fringes are same 3.) Interference fringes either of the same size or decrease after moving away from the center. 4.) Dark fringes are usually perfectly dark. 5.) A minimum coherent source is needed. Diffraction: 1.) It occurs due to secondary wavelets, originating from infinite different points of the same wavefronts. 2.) Central maxima of bright fringe is followed by either side maxima of decreasing intensity. 3.) Interference fringes are never of the same shape and size. 4.) Dark fringes are not perfectly dark. 5.) It is possible by either one or more than one source which need not be coherent.

Superconductivity The property of a substance in which the electrical resistance of the substance is zero at very low temperatures. This property of substance is called superconductivity. For certain substances, like mercury, the resistivity suddenly drops to zero at very low temperatures typically near the boiling point of liquid helium. Some metals, doped semiconductors, alloys and ceramics (i.e. these are insulators at room temperature and superconduct at higher temperatures than the metals) show superconductivity. Temperature Dependence of Resistivity In superconducting substances, the resistivity suddenly drops to zero at a particular temperature known as critical temperature ($T_{c}$) or transition temperature and remains zero below that as shown in Figure below. The critical temperature for mercury is $4.2 K$. Below this critical temperature, mercury is superconducting whereas above this temperature it behaves like a normal conductor. Different superconducting

German scientists R.Classius and J.C. Maxwell had propounded the kinetic theory of gases. According to this model, every gas is made up of very fine particles called molecules. All the molecules of a gas are similar in all properties. We know that $ 1 cm^{3}$ of water at $100^{\circ}C$ temperature and $1$ atmosphere pressure produces $1671 cm$ of water vapour. From this, it is known that the volume actually occupied by the molecules in $1671 cm^{3}$ of water vapour is only $1 cm^{3}$ and the remaining $1670 cm^{3}$ of volume is empty. In other words, we can say that in the gaseous state of matter, there is a lot of free space between the molecules. This fact is true for all gases. The molecules of gases are always moving randomly in all possible directions. During motion, these molecules collide with each other and with the walls of the vessel in which the gas is kept. After each collision, both the direction and speed of motion of these molecules keep changing. All collisions betw