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Question Video: Identifying How a Convex Lens Changes the Path of Parallel Rays of Light Science

Which of the following diagrams shows what happens when parallel light rays pass through a thin convex lens? [A] Diagram A [B] Diagram B [C] Diagram C [D] Diagram D [E] Diagram E

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Video Transcript

Which of the following diagrams shows what happens when parallel light rays pass through a thin convex lens? (A), (B), (C), (D), or (E).

In this question, we are being asked to identify the diagram that correctly shows the path of light rays that pass through a convex lens. We are given five diagrams where parallel rays of light are incident on convex lenses. We’re being asked what happens to the light rays next when they leave the lens. Let’s first remember what we know about convex lenses and draw a diagram showing their key features.

First, let’s draw in the optical axis. The optical axis is an imaginary line that passes through the widest part of a convex lens. When rays of light entering the lens are parallel to the optical axis, like this, the lens causes the rays to converge. This means that the light rays change direction and move closer together. The light rays meet at a single point on the optical axis of the lens, called the focal point.

Now let’s compare this to the diagrams we have been given in this question. We can see that in all of these diagrams, parallel rays of light are entering the lens.

In option (A), the lens has no effect on the direction of the light rays, with all the rays remaining parallel after they leave the lens. So, this cannot be the correct answer.

In option (B), the lens changes the direction of the light so that the light rays converge at a single focal point along the line of the optical axis. This matches our earlier description of what should happen when light passes through a convex lens. So, option (B) is a good candidate for the correct answer.

In option (C), the lens changes the direction of the rays so that they move further apart and spread out. This is also called diverging. These rays will never meet at a single point, so this cannot be the correct answer.

In option (D), the lens changes the direction of all the light rays by the same amount. Even though the light rays have changed direction, they are still parallel after they’ve passed through the lens. Again, these light rays will never meet at a single point. So, this cannot be the correct answer.

Finally, in option (E), the lens causes the light rays to move closer together. However, the rays do not all meet at a single point. Three of the rays meet here, but this fourth ray doesn’t. There is no single point that all the rays pass through. So, this diagram cannot correctly show the effect of a convex lens.

That leaves us with option (B). This correctly shows the convex lens causing the rays to converge at a single point. So, option (B) is the correct answer.

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