The produced rays in sonography are 

At what speed should a galaxy move with respect to earth so that the sodium light at $589 \mathrm{nm}$ is observed at $589.6 \mathrm{nm}$?

A galaxy is moving away from the earth at a speed of $286 \mathrm{km} {\mathrm{s}}^{-1}$. The shift in the wavelength of a red line at $630 \mathrm{nm}$ is $x\times {10}^{-10} \mathrm{m}$. The value of $x$, to the nearest integer, is ___ .

[Take the value of the speed of the light $c$, as $3\times {10}^8 \mathrm{m} {\mathrm{s}}^{-1}$]

Write short notes on any two of the following:

(i) Diffraction.

(ii)Doppler effect

(III) Polarisation of wave