# If light cannot bend, then how magnify glass works?

## Main Question or Discussion Point

i don't understand if light cannot bend, then how magnify glass works?
how it is bending & magnifying the light?

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phinds
Gold Member
2019 Award
i don't understand if light cannot bend, then how magnify glass works?
how it is bending & magnifying the light?

if light cannot bend then how refraction & reflection of light are working?
is it still mystery or any other theory is there for this?

phinds
Gold Member
2019 Award
if light cannot bend then how refraction & reflection of light are working?
is it still mystery or any other theory is there for this?

i am asking if light can not bend, how REFRACTION is done ?

Dale
Mentor
Who says a ray of light does not bend?

how medium can bend the light?
water is bending the light everytime. is it mystery?

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

if we throw the ball it will bounce, when it touches the ground, so same way, the light bounces back that bounce of light is called refraction, am i right?

Dale
Mentor
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.

think of a vehicle which rolls at an oblique angle: means vehicle going down mountain slope down, then it will go fast, because slope down will increase the velocity of vehicle. same way refraction will increase the speed of light ray like speed of vehicle increased by mountain slope through mechanical analogy.

Dale
Mentor
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?

of course any two wheeler or four wheeler vehicle will get spoiled, due to rough end due to heavy friction. sorry, but it doesn't explains about light.As you said it will bend due to different medium, wiki is showing light bend due to surface phenomenon, i am confused. so light bends because of two reasons: surface phenomenon & different medium? what i understand about light bend is right or wrong?

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Dale
Mentor
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.

will it travel straight or will it tend to turn one direction or the other? it depends on driver's experience. of course anybody can change vehicle direction due to steering. it works under steering gear mechanism. but light is electromagnetic waves. it carries energy every time.
vehicle direction is depends on driver mindset.
so due to Maxwells equations, light is bending & bounces back?

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Dale
Mentor
will it travel straight or will it tend to turn one direction or the other? it depends on driver's experience.
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?

Dale
Mentor
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.

thank you it explains lot, but what i understand is there is no theory to explain or demonstrate why light refraction & reflection.

Dale
Mentor
I already told you that the theory is Maxwells equations.

Drakkith
Staff Emeritus
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.

thank you it explains lot, but what i understand is there is no theory to explain or demonstrate why light refraction & reflection.
I have no idea why you believe this. It is utterly wrong. Refraction and reflection are understood extremely well.

DaveC426913
Gold Member
It may be helpful to recognize that a light beam is not zero width. It is not a one dimensional line intersecting the surface.

The light beam has a width it is a wavefront, and parts of it reach - and interact with - the surface at different times. So, one edge of the light beam slows down passing through the medium before the other.

There's more to it..

It may be helpful to recognize that a light beam is not zero width.
.
pardon me, i am not asking light has width,dimensions or not.

phinds
Gold Member
2019 Award
pardon me, i am not asking light has width,dimensions or not.
Yes, Dave completely understands that you were not asking that, he was giving you another helpful way to see what is happening. You really seem determined to not understand that refraction is no big mystery.

DaveC426913
Gold Member
pardon me, i am not asking light has width,dimensions or not.
You are asking how it refracts.

In the car/road analogy, the car will veer off the road in essence because the car is non-zero width, meaning the two front tires hit the mud at different times. A motorcycle, being essentially one dimensional, has only one front wheel to hit the mud, so no delay.

The car/road analogy breaks down quickly, but maybe it will get the idea across.

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And it continues out the other side, both wheels in dirt to right wheel back on pavement pulls back to the direction the car was travelling offset by the distance thru the refractive medium. That's for straight lanes, like flat glass. Lenses as you might guess change the angle your wheels hit dirt.