Ray Optics And Optical Instruments

by lens formula

Given and



Hence, power of lens is

Wavelengh

or $\lambda_{2}=\frac{3}{4} \lambda_{1}=\frac{3}{4} \times 4200=3150\, ??

The atmosphere can be considered to consist of a number of parallel layers of air of different densities and therefore of different refractive indices. The density and the refractive index of layers decrease with altitude.

The rays of light coming from a star to the earth are thus continually refracted from the rarer to the denser layers and so they bend slightly towards the normal at each refraction from one layer to the next. Thus, they follow a curved path and reach the eyes of the observer at as shown in figure. Hence, the image of the star is seen as . But due to the wind and the convection currents in air the density of layers keep on changing and hence, the position of the star as seen, keeps on changing. These different images of the star give an impressinn to an observer that the star is twinkling.

For a given prism, the angle of deviation depends upon the angle of incidence of the light rays falling on the prism.
Taking triangle FQR, we have

Focal length in air is given by,

The focal length of lens immersed in water is given by

where are radii of curvatures of the two surfaces oflens
and is refractive index of glass with respect to liquid.

Also

Given,