Lens Magnification
For a paraxial thin lens, m = h_i/h_o = v/u. Negative m denotes an inverted image and positive m an erect image.
Why this shows up in the exam
Image-size prediction · Microscope objective calculations · Projection scaling
Learn the idea
A thin lens's transverse magnification is the signed ratio of image distance to object distance. The same ray triangles that set image position also set image height and orientation.
🧠 Memory hook: Lens magnification has no extra minus: m = v/u.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- m = h_i/h_o = v/u — signed transverse magnification for a thin lens
How to approach it
- 1Determine signed u and v
- 2Compute m = v/u
- 3Use sign for orientation and magnitude for scale
Common slip-ups that cost marks
- •Importing the mirror minus sign
- •Treating sign as physical height magnitude
- •Multiplying distances instead of taking their ratio
🌟 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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