Q1. [4]
The above ray diagram is to show image formation by a reflecting telescope. Reflecting telescope revolutionized our way of looking into the sky. Reflecting telescopes employ large mirrors to gather and focus light rather than relying solely on lenses as we do in the refracting telescopes. These telescopes utilize precisely shaped and polished mirrors to capture incoming light and reflect it to a focal point, where the telescope forms an image for observation.
The above ray diagram is to show image formation by a reflecting telescope. Reflecting telescope revolutionized our way of looking into the sky. Reflecting telescopes employ large mirrors to gather and focus light rather than relying solely on lenses as we do in the refracting telescopes. These telescopes utilize precisely shaped and polished mirrors to capture incoming light and reflect it to a focal point, where the telescope forms an image for observation.
Answer the following :
- (a) What kind of image of a star is seen by the observer in the eye-piece ? [1]
- (b) What kind of mirror is used in this reflecting telescope ? [1]
- (c) Explain with the reason, what kind of optical device (type of lens or mirror) is used at the eye-piece. [2]
Previously asked in CBSE board exam
2026 31/4/1 Q38
Generated by claude-sonnet-4-6 · 2026-06-15 06:47 · grounding stimulus
Model Answer
(a) The observer sees a virtual, erect, and magnified image of the star in the eyepiece.
(b) A large concave mirror (primary mirror) is used in the reflecting telescope to gather and focus incoming light.
(c) A convex lens is used at the eyepiece. The reason is that the concave mirror forms a real image of the distant star at its focal point. This real image acts as a virtual object for the convex lens (eyepiece), which then forms a magnified, virtual, and erect image for the observer to view comfortably. A convex lens thus acts as a magnifier.
Source: Light – Reflection and Refraction / The Human Eye and the Colourful World, Optical Instruments section
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Explanation
- (a): The eyepiece always acts as a simple microscope producing a virtual, erect, magnified image — examiners expect all three characteristics.
- (b): The key word "large concave mirror" must appear; "large" matters because it gathers more light (better resolution).
- (c): 2 marks means you need both the correct answer (convex lens) and the reason (it acts as a magnifying glass on the real image formed by the mirror). Stating only the type without reason will lose 1 mark.
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