Question Video: Identifying the Path of a Light Ray Reflected from a Convex Mirror Science

The ray diagram below shows different paths taken by parallel rays after they reflect off a convex mirror. Which one of the paths is correct? [A] Path 1, because a convex mirror will not focus the incident light at a point [B] Path 2, because a convex mirror will focus the incident light at a point

02:05

Video Transcript

The ray diagram below shows different paths taken by parallel rays after they reflect off a convex mirror. Which one of the paths is correct? (A) Path 1, because a convex mirror will not focus the incident light at a point. (B) Path 2, because a convex mirror will focus the incident light at a point.

In this problem, we’ve been given a convex mirror and rays of incident light that are parallel to the optical axis of the mirror. Both of these rays are initially traveling along the same path. Hence we’ve been told they’re parallel. One of these rays is reflected off the mirror along path 1, and the other is reflected along path 2. But only one of these correctly shows how a light ray actually reflects off a convex mirror. We need to figure out which one that is.

To answer this question, let’s remember an important fact about convex mirrors. Let’s recall that any ray of light that is traveling parallel to the optical axis of a convex mirror will be reflected off the mirror in a very specific way. We can trace backward the reflected ray of light to see that it appears to come from this point here on the optical axis. This point is known as the focal point. And any other incident ray of light that is parallel to the optical axis will also be reflected so that it appears as if the reflected ray is coming from the focal point.

It’s important to remember though that reflected rays only appear to be coming from the focal point. In reality, they are all being reflected off in different directions from the surface of the mirror, and so are not all being focused at one point after being reflected.

Knowing this, we can see that our incident ray of light cannot be reflected along path 2, because if we trace this path back, then it does not cross the optical axis on the other side of the mirror. If we do this for path 1 though, we see that this is exactly what we’re looking for.

Our final answer is option (A). The light ray is reflected along path 1.

Nagwa uses cookies to ensure you get the best experience on our website. Learn more about our Privacy Policy.