# Physics I

## What are dextrorotatory and laevorotatory substances?

Dextrorotatory and laevorotatory substances are optically active substances. Dextrorotatory  substances Substances which rotate the plane of polarization of the light towards the right are known as dextrorotatory substances. Laevorotatory substances Substances which rotate the plane of polarization of the light towards the left are known as laevorotatory substances.

## What is optical activity?

Optical activity Optical activity is the ability of a substance to rotate the plane of polarization of plane polarized light. Substances which have this ability are called optically active substance. Tartaric acid is an example of optically active liquid. Explanation When a polarizer and analyzer are crossed, no light emerges out of the analyzer. When …

## What is nicol prism?

Nicol prism Nicol prism was invented by William Nicol in 1828. It is an optical device used for producing and analyzing plane polarized light. The nicol prism is made in such a way that it eliminates one of the two rays by total internal reflection. It is generally found that it eliminates the ordinary ray …

## What do you understand by double refraction?

Double refraction Erasmus Bartholinus discovered in 1669, that, when a ray of light is refracted by a crystal of calcite it gives two refracted rays. This phenomenon is called double refraction. Calcite is crystallized calcium carbonate (CaCO3). It crystallizes in many forms and can be reduced by cleavage or breakage into a rhombohedra.

## Define phase velocity and group velocity?

Phase velocity Phase velocity is the velocity with which a plane progressive wave front travels forward. Phase velocity is symbolized by . It has a constant phase =  Group velocity The group velocity () is the speed with which the point of reinforcement of the resultant wave travels. The group velocity is different from the individual …

## What do you mean by phase angle and epoch?

Phase angle Phase angle is defines as the fraction of the time interval that has lapsed since the particle has crossed the mean position of rest in the positive direction. It is also equal to the angle swept by the radius vector since the vibrating particle last crossed its mean position of rest. For a …

## What is wavelet and secondary wavefront?

Wavelet: Wavelets are tiny parts of waves. Secondary wavefront: The envelop of all the secondary wavelets in the forward direction is called the secondary wavefront. The backward envelop is not a secondary wavefront.

## Define wavefront?

Wavefront A wavefront can be defined as the locus of all the points of the medium which are vibrating in phase and are also displaced at the same time. If the distance of the source is small the wavefront is spherical. But when the distance is large then any small portion of the wavefront can …

## What is diffraction grating?

Diffraction grating Diffraction grating is an extremely useful device. In one of its form it consists of a very large number of narrow slits side by side. The slits are separated by opaque spaces. Diffraction gratings are of two types; transmission grating and reflection grating. Transmission grating: When a wavefront is incident on a grating …

## What do you mean by Fresnel and Fraunhofer class of diffraction?

Diffraction phenomena can conveniently divided into two groups. Fresnel Diffraction Phenomena: In the Fresnel class of diffraction, the source or the screen or the both are at finite distances from the aperture or obstacle causing diffraction. In this case, the effect at a specific point on the screen due to the exposed incident wavefront is considered …

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