Aparticular hene laser beam at 633 nm has a spot size of 0.8 mm. assuming a
gaussian beam, what is the divergence of the beam? what are its rayleigh range and beam width at 10
m?

Alead ball is dropped into a lake from a diving board 5m above the water . it hits the water with a certain velocity and then sink with constant velocity in bottom . it reaches the bottom 5 second after it is dropped if g= 10m/s2 . find depth of the lake and average velocity of the ball ?