If focal length halves from 8 cm to 4 cm, what happens to the angular magnification M ≈ 25 / f?

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Multiple Choice

If focal length halves from 8 cm to 4 cm, what happens to the angular magnification M ≈ 25 / f?

Explanation:
Angular magnification from a simple magnifier scales inversely with the focal length. With M ≈ 25 / f (f in cm), halving the focal length doubles M. If f goes from 8 cm to 4 cm, M changes from 25/8 ≈ 3.13 to 25/4 = 6.25, which is a doubling. The intuition is that a shorter focal length lens bends light more strongly, making the image appear larger to the eye at the near point.

Angular magnification from a simple magnifier scales inversely with the focal length. With M ≈ 25 / f (f in cm), halving the focal length doubles M.

If f goes from 8 cm to 4 cm, M changes from 25/8 ≈ 3.13 to 25/4 = 6.25, which is a doubling. The intuition is that a shorter focal length lens bends light more strongly, making the image appear larger to the eye at the near point.

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