In high school students are told about the ability of spherical mirror to converge parallel beam of light falling to it at the focus at the same time they are told about the limitation of spherical aberration and a parabolic mirror would remove it but are never told how would a parabolic mirror converges all the rays at the focus. Want to know the proof ??

Newton’s Universal Law of gravitational force states that the force of attraction between two point masses is directly proportional to the product of masses and inversely proportional to the square of distance between them. But can we apply the same principle to calculate the force between massive bodies, for some mass will be closer from the center and some will be far from the center.

[PDF] Let us look at the Proof

This is a video demonstrating the formation of stationary wave. Stationary wave in particular because it includes both the concept of travelling waves and stationary wave. You can download the video and use for your own e.

The smaller file size showing similar demonstration made by using qbasic is available here.

[.EXE] Standing wave demonstration.