You are given two convex lenses: Lens P has a short focal length and Lens Q has a long focal length. Both are…

Question

You are given two convex lenses: Lens P has a short focal length and Lens Q has a long focal length. Both are held in sunlight. For which lens will the sharp image of the Sun form closer to the lens, and why?

Accepted Answer

## Model Answer **Lens P** (short focal length) will form the sharp image of the Sun closer to the lens. A convex lens forms the image of a distant object (like the Sun, which is at infinity) at its principal focus F₂. The shorter the focal length, the closer this focus is to the lens. Since Lens P has a shorter focal length than Lens Q, its image forms nearer to the lens. *Source: Chapter 9, Table 9.4 — Image at focus F₂ when object is at infinity.* ## Explanation - The key concept is: **object at infinity → image at focus**. This comes directly from Table 9.4. - Examiners award 1 mark for identifying **Lens P** and 1 mark for the reason (shorter focal length = focus closer to lens). - Don't just say "focal length is less" — link it to *where the image forms* (at the focus).

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