13. 1.To find out velocity of moving object. 2.Discovery of Saturn’s rings as swarm of particles and not solid discs. 3.Discovery of spin of the sun. 4.Discovery of binary stars. 5.To find out whether a star is moving towards the earth or moving away from the earth. 6.Discovery of receding of galaxies from each other.
15. A Source which emits sound waves of frequency 1600 Hz and an observer approach one another with a relative velocity of 80 m/s. Calculate the increase or decrease in the frequency.