Louis La Minh Hoang

Today’s physics lesson was all about lenses — not just the theory, but the actual skill of drawing accurate ray diagrams. Even though I’ve learned about lenses before, this session pushed me to be much more precise and systematic with every construction.

We started by revisiting the two main types of lenses: convex (converging) and concave (diverging). But the real focus was on how to draw the images correctly, using the standard principal rays. Instead of guessing or sketching loosely, we practiced the exact steps: drawing the principal axis, marking focal points, positioning the object, and constructing rays with strict rules. Every line mattered.

For convex lenses, I practiced the three essential rays: the one parallel to the axis, the one through the focal point, and the one passing through the optical center. It’s crazy how just combining two of them already gives you the exact image point. We worked through all the classic object positions — twice the focal length, between f and 2f, inside f — and each case produced something different: inverted, magnified, reduced, or even virtual.

For concave lenses, the challenge was understanding how the rays diverge and how the image forms by extending them backward. Drawing virtual images requires more care, because the rays don’t actually meet; you have to extend them cleanly, so the diagram stays accurate.

What made today advanced wasn’t the formulas — it was the precision. We solved problems where even a small mistake in ray placement could produce a completely wrong image. Some diagrams involved measuring exact distances, matching scales, and explaining the image characteristics based on geometry alone.

By the end, I felt a lot more confident. Instead of memorizing “the image is inverted” or “the image is magnified,” I could actually prove it through clean constructions. Today wasn’t just learning about lenses — it was learning how to think like someone drawing real optical systems.