Question

can someone explain the concept of refraction?

Answer 1

one way to think of this is the following: light is a wave which travels at the speed og light (3 x 10^8 m/s) when it is in vacuum. When it enters another medium, like glass, it slows down. Picture a long wave crest approaching the beach at an angle. if the left side of it slows down, maybe because the water is getting shallow, while the right side continues to travel, it will appear that the wave is changing direction. This is an analog of what happens with light... it slows when it enters an optically more dense medium, wnd thus changes the direction of its motion. That change in direction is called refraction

Answer 2

The change of direction of a light ray during refraction is best explained by the wave-like analogy of light. You can consider the Huygens principle of wavelets, in which a wavefront propagates through a medium by creating spherical waves from every point along the wavefront. These constructively and destructively interfere in such a wave as to generate the next wave front and cancel out the components in other directions on average (except at the outer edges of the wavefront, which have nothing to completely cancel their sideward-moving wave components. This is diffraction but this effect is quite small whilst simply passing through a medium rather than through an aperture). So the wave continues to propagate wavefront by wavefront through the transparent medium and eventually reaches the boundary between two materials at a non-perpendicular angle. The first part of the wave to reach the boundary creates a new wavefront within the new material that propagates at a different speed to that of the original medium. The rest of the wave continues to travel through the original medium for longer than the part of the wave that reaches the boundary first. This difference means that the wavefront has some parts of it moving faster than other parts of it along the length of the wavefront. If you sustain this for a certain period of time (the time taken for a given width of wavefront to enter the new material), then the wave will take on a new angle. This is the new angle of the wavefront. This new wavefront, now in the new material, will generate a new set of spherical wavelets that propagate from the wavefront, however the direction on which there will now be greatest constructive interference is actually perpendicular to the newly angled wavefront, not in the previous direction. So the direction of light propagation and energy transfer has been changed by an intereference effect from the millions of spherical wavelets that radiate out from the wavefront.