Question Video: Identifying the Greatest Radius of Curvature for Concave Lenses | Nagwa Question Video: Identifying the Greatest Radius of Curvature for Concave Lenses | Nagwa

# Question Video: Identifying the Greatest Radius of Curvature for Concave Lenses Science • Third Year of Preparatory School

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The diagram shows five concave lenses. Which lens has the greatest radius of curvature?

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### Video Transcript

The diagram below shows five concave lenses. Which lens has the greatest radius of curvature?

This question asks us which of the lenses shown has the greatest radius of curvature. We can see that all these lenses are concave lenses.

First, let’s remember that a concave lens can be formed like this, with a cylinder and two spheres in such a way that the intersection of all of them forms the concave lens. The radius of each of the spheres is the radius of curvature of the concave lens. The larger the radius of the spheres, the larger the volume of the spheres will be, and so the thinner the lens is at the top and the bottom. That is, a larger radius of curvature means a concave lens that is thinner at the top and bottom. Or we could equally flip that statement around to say that a concave lens that is thinner at the top and bottom is a lens that has a larger radius of curvature.

Let’s now look at the five lenses we’re given in the question. We can draw in one of the spheres that forms the concave lens for each of the five lenses we are given. Then, using these spheres, we can easily identify the radii of curvature for lenses 1, 2, and 5. Lenses 3 and 4 are clearly formed from spheres that are larger than 1, 2, and 5. We cannot easily fit the full spheres on screen in these cases to add the radii of curvature. However, we can note that lens 4 is the thinnest at the top and bottom and the part of the sphere we have drawn in for this lens appears less curved than that for lens 3, and indeed all the other lenses.

So the concave lens made up from the largest spheres, or the lens with the largest radius of curvature, is lens 4. Therefore, our answer to the question is lens 4.

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