23.2 Lenses | General Physics

Chad provides a thorough lesson on Thin Lenses that includes both Converging Lenses and Diverging Lenses. A real image is the result of the refracted rays intersecting at a common point after passing through the lens. A virtual image results when the refracted rays do not intersect at all, but appear to have originated from a common point from the back side of the lens. Images may also be either upright or inverted as well, and for images resulting from a single lens, real images are always inverted, and virtual images are always upright. The focal distance is still defined as one half the radius of curvature, just as it was for spherical mirrors, and the thin mirror equation also applies to thin lenses and is therefore also referred to as the thin lens equation or mirror and thin lens equation (1/p + 1/q = 1/f).

The lesson begins with converging lenses. If the object distance is greater than the focal length, then a real, inverted image results. If the object distance is less than the focal length, then a virtual, upright image results. For a diverging lens, the image is always virtual and upright regardless of where the object is placed relative to the focal point.

Chad shows how to draw 3 different incident and refracted rays in order to construct a proper ray diagram, and how this ray diagram can be used to understand why and when an image is either real and inverted or virtual and upright. Chad shows how to draw these 3 rays for both converging and diverging mirrors.

Chad concludes the lesson by solving several Lenses calculations involving the Thin Lens equation as well as the magnification equation.

00:00 Lesson Introduction
01:12 Introduction to Thin Lenses
03:55 How to Draw Ray Diagrams for Thin Lenses
09:44 Calculations for Thin Lenses (Thin Lens Equation and Magnification)
15:01 Combinations of Lenses
21:57 Lens Power
23:38 The Human Eye (and How to Correct for Hyperopia and Myopia)

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