Simple Microscope and Angular Magnification
For a convex magnifier of focal length f, angular magnification is D/f for final image at infinity and 1+D/f for final image at the near point D.
Why this shows up in the exam
Reading magnifiers · Jeweller's loupes · Field inspection lenses
Learn the idea
A simple microscope lets a small object be held closer than the unaided near point while keeping a comfortable virtual image. The lens does not need a large linear image; it increases the angle the object subtends at the eye.
🧠 Memory hook: Relaxed eye gives D/f; near point adds one.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- M_infinity = D/f — relaxed eye, final image at infinity
- M_near = 1 + D/f — final image at least distance D
How to approach it
- 1Identify infinity or near-point adjustment
- 2Choose the matching magnification formula
- 3Keep D and f in the same unit
Common slip-ups that cost marks
- •Using linear magnification as angular magnification
- •Forgetting the final-image condition
- •Using centimetres inconsistently for D and f
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A real object is placed 30 cm from a converging lens of focal length 10 cm. Find the real image distance.
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