Why doesn't a biconvex lens cancel itself out and not change the light beam?

[theonlywalks]

When you have a biconvex, i.e. two convex lens' back to back, doesn't the light beam just come out straight?

Since one convex lens is back to back with another, essentially it is a convex lens, followed by a concave lens. The light would first hit the convex lens, and the light would converge. Then the light would hit the concave lens, and the light would diverge.

This is what happens when the light ray hits each of these independently, yet for some reason when they are back to back (i.e. a biconvex lens) the light gets super converged.

I would think that the light would converge, then it would diverge, and thus be back to what it was originally.

If you take a convex lens and it converges the light coming onto it, then if you flip the lens so the light is coming in the opposite side, the light would diverge would it not?

 

[theonlywalks]

really, no one knows the answer lol?

 

[Bob S]

Open this lens simulation program from the University of Colorado

http://phet.colorado.edu/en/simulation/geometric-optics

and click on the green RUN NOW box in the lower right. Adjust the lens curvature, diameter, and index of refraction.

Bob S

 

[sophiecentaur]

When you have a biconvex, i.e. two convex lens' back to back, doesn't the light beam just come out straight?

Since one convex lens is back to back with another, essentially it is a convex lens, followed by a concave lens. The light would first hit the convex lens, and the light would converge. Then the light would hit the concave lens, and the light would diverge.
etc

You only have to look at any simple lens / ray path diagram to see that you can't possibly be right. What 'cancelling out effect' is there? If you turn right then turn right again, you don't end up going straight!
If in doubt look at Google / Wikkers

 

[sardar]

This is a common misconception about biconvex lenses. When two convex lenses are placed back to back, the light beam does not simply come out straight. This is because the two lenses do not cancel each other out, but rather they work together to change the direction of the light beam.

Each lens has its own focal length and refractive index, which determines how it bends the light passing through it. When two lenses are placed together, the first lens bends the light and the second lens further bends the already bent light. This results in a more significant change in the direction of the light beam.

Furthermore, the two lenses must be perfectly aligned and have the same curvature in order to cancel each other out. In most cases, this is not possible and there will always be some degree of change in the light beam.

Moreover, the distance between the two lenses also plays a role in the final direction of the light beam. If the lenses are too close together, the light will not be able to diverge enough before reaching the second lens, resulting in a more converged beam. On the other hand, if the lenses are too far apart, the light will diverge too much and may not even reach the second lens.

In summary, a biconvex lens does not cancel itself out because each lens has its own unique properties and the alignment and distance between the lenses also play a crucial role in the final direction of the light beam.