What is meant by the statement "critical angle for diamond is 24 degree"?

When a light Ray travels from a dence medium to a rare medium, the ray gets refracted. At some angle of incidence the refracted ray travels on the surface between the 2 mediums. This angle (in the dence medium) making the refracted ray to travel on the surface is called the critical angle.

The critical angle is produced for the maximum angle the ray can produce in the dence medium without being totally internally reflected.

And for different materials the critical angle takes different values. The critical angle for a diamond in air is 24 degrees

( while the critical angle for glass is 41 degrees.)

Hope this helps.

russian is not my first language, so i'm afraid i can't write out an answer in russian, but hopefully you can find a way to do so. here's my best translation of the problem: you're given a plot of a particle's position in one-dimensional space over time, and you're asked to find either the total distance traveled by the particle after 6 seconds had elapsed, or the total displacement of the particle after 6 seconds.

if you want the total distance traveled, you would first need to determine the particle's velocity as a function of time, then integrate that over the 6-second interval. we know the position function is quadratic with roots at 0 and 6, so we have

where is unknown. because the position is parabolic, there is symmetry about the midpoint at , and we know that

so that the position function is

which means the velocity is

then the total distance traveled is

so the total distance traveled is 20 m.

on the other hand, if you want to find displacement: the particle starts at and ends at , so its displacement is 0.