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Question Video: Identifying a Rotated Concave Lens Science

Which of the following is a concave lens? [A] Shape (A) [B] Shape (B) [C] Shape (C) [D] Shape (D) [E] Shape (E)


Video Transcript

Which of the following is a concave lens? (A), (B), (C), (D), or (E)?

In this question, we are asked to choose which picture shows a concave lens.

Let’s first think about what we know about concave lenses. When viewed from the side, a concave lens has this shape. The outline of a concave lens can be drawn using a cylinder and two spheres viewed from the side. If we overlap these shapes like this, we can see the shape of the concave lens. The lens is thinner in the middle and thicker at the edges, with two curved sides.

To answer this question, we need to decide which option is a concave lens. We can automatically discard shapes (B) and (D). These are thicker in the middle and thinner at the edges, so these cannot be convex lenses.

Similarly, we can rule out option (D). Option (D) is thicker on the right side than in the middle, and thinner on the left side than in the middle. This is not the shape of a concave lens.

Now let’s look at option (A). This shape is thicker at the edges than in the middle. But the edges are straight, not curved, so this is not right.

We are left with option (C). We can see that it is thinner in the middle than at the edges and that these edges are curved. This can also be drawn using a side view of two spheres, like we described earlier. So this is a concave lens. The correct answer is option (C).

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