If light cannot bend, then how magnify glass works?

Who says a ray of light does not bend?

 

It is not a mystery. Refraction is caused by a change in the speed of light at the interface of two different transparent media.

 

That is reflection. Reflection and refraction are different.

If you want a mechanical analog of refraction think of a vehicle which rolls at an oblique angle from a smooth road onto a rough road.

 

Forget the slope of the mountain, consider the road to be level. What happens when a vehicle rolls from a smooth road onto a rough road?

 

OK, now, before it gets spoiled, will it travel straight or will it tend to turn one direction or the other?

Of course it doesn't explain, it is an analogy, not an explanation. The explanation is Maxwells equations.

 

No. The tendency of the vehicle is a matter of physics. An experienced driver can compensate for what the vehicle tends to do, but that does not change the physics.

Again, what does the vehicle tend to do?

 

It seems like you have left for the time being, and in an hour or so I will have to also, so I will answer my own question and then give an explanation from Maxwells equations.

If there is rough road to the right and a vehicle goes from smooth road onto the rough road then it will tend to pull to the right. This will happen as soon as the right tire hits the rough road and is slowed down compared to the left tire which is still going on the smooth road. Analogously, light will turn if it goes into a medium with a slow speed of light (analogous to the rough road).

One of the simplest solutions to Maxwells equations is a single frequency plane wave. If you take two such solutions, one for each material, and match them at the interface, then you will get that the propagation direction is different in each.

 

I already told you that the theory is Maxwells equations.

 

Let's do away with analogies here, I don't think they will help. Light is NOT a ray that travels in a straight line. It is an electromagnetic wave. A ray is a simplification that makes it easier to calculate what the light will do in certain situations, such as what happens when it enters a lens or hits a mirror.

Refraction is a property that all types of waves have. When a wave enters a medium where the speed of the wave is different, it changes direction unless it enters the new medium straight on at a 90 degree angle. The reason why this happens is hard to grasp but has to do with how different parts of the wave interfere with each other while the wave moves across the boundary.

I have no idea why you believe this. It is utterly wrong. Refraction and reflection are understood extremely well.