An object is moved steadily from a very large distance towards the pole of a concave mirror. How does the position of the real image change as the object moves from beyond C to exactly at F? Describe the trend clearly.
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Model Answer
As the object moves from beyond C towards F, the real image shifts continuously away from the mirror (i.e., beyond C, further and further from it), and becomes progressively larger (more enlarged).
Specifically:
- Object beyond C → Image forms between F and C; diminished, real, inverted.
- Object at C → Image forms at C; same size, real, inverted.
- Object between C and F → Image forms beyond C; enlarged, real, inverted.
- Object at F → Image shifts to infinity; no image is formed on a screen.
Thus, as the object moves from beyond C to F, the image moves from between F and C to infinity, and its size increases from diminished to infinitely large.
Source: Chapter 9, Section 9.2.1, Table 9.1
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Explanation
- The examiner expects you to clearly describe the trend (image moves farther away, becomes larger) as well as the specific positions from Table 9.1.
- Mention all four stages: beyond C, at C, between C and F, and at F — this covers the full range asked.
- Key phrase to remember: image moves from between F and C → to C → beyond C → infinity as the object moves from far beyond C toward F.
- The nature remains real and inverted throughout (except at F, where no image is formed).