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Question Video: Recognizing Incident Rays and Reflected Rays Science

The figure shows a group of parallel light rays incident on and a group of light rays reflected from a concave mirror. In which group do all the light rays pass through point 𝑃?

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Video Transcript

The following figure shows a group of parallel light rays incident on and a group of light rays reflected from a concave mirror. In which group do all the light rays pass through point 𝑃? (A) The incident light rays only. (B) The reflected light rays only. (C) Both the incident light rays and the reflected light rays. (D) Neither group of rays.

We want to know whether the incident light rays, the reflected light rays, or none, or both groups of light rays pass through this point, 𝑃. We see that of the three incident rays, red, green, and blue, only the ray depicted by the green line passes through point 𝑃. This means that option (A) and option (C) are incorrect.

The green incident ray travels along the optical axis of the concave mirror. Therefore, the green reflected ray will be reflected back along its incoming path and will pass through point 𝑃. For the red and blue incident rays, they hit these points on the concave mirror, and we see that the reflected rays pass through point 𝑃. So, all three reflected rays pass through point 𝑃, and we’ve already seen that not all three incident rays do.

Therefore, the answer must be option (B). The group in which all the light rays pass through point 𝑃 is the reflected light rays only.

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