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00:00 Introduction to convex lenses/converging lenses: refraction through a converging lens, focal point and power of the lens in diopters.
02:31 Finding the focal length of a convex lens: focus an image with the lens. Focal point vs. focal plane.
04:00 Principal rays for a converging lens: how to choose the rays for a ray diagram.
04:45 Ray diagrams, image distance for convex lenses: object outside the focus vs. object inside the focus. Ray diagrams from principal rays to find the image. Real and virtual images formed by a convex lens.
08:01 Time to get quantitative with lenses! Definitions and sign conventions for the thin lens equation and magnification equation: object distance, image distance, focal length, thin lens equation, magnification in terms of image height and object height, magnification in terms of image distance and object distance (phew!).
10:03 Quantitative examples of images formed by convex lenses/converging lenses: focus and object distance are given, apply the thin lens equation to find the image distance, magnification.

In this introduction to convex lenses/converging lenses: focus, ray diagrams, image distance, magnification are all introduced. We start by discussing the refractions in the lens that cause parallel rays to converge to a focal point, and we include a quick note on optical power. Next, we talk about how to experimentally find the focal length of a convex lens and we distinguish focal point vs. focal plane. Next, we discuss the principal rays for a converging lens that are useful to us when we try to find the image formed by a convex lens, then we construct qualitative ray diagrams for the two main cases with convex lenses: object outside the focus vs. object inside the focus. We distinguish between the real image formed in the first case and the virtual image formed in the second case. Next, we introduce all the definitions and sign conventions for thin lenses: object distance, image distance, focal length, image height and object height. We introduce the thin lens equation which allows us to quantitatively find the image distance, and the magnification equation which allows us to quantitatively determine the magnification and orientation of the image in terms of the image distance and object distance. Finally, we work two examples of images formed by a convex lens. We use the thin lens equation to find the image distance and the magnification equation to find the magnification and orientation of the image. In the first case, the object is outside the focus, and in the second case the object is inside the focus.

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