Thin Lenses

The following videos will define the two primary types of lenses you need to understand, converging and diverging, and how to draw ray diagrams for them.

Thin Lens Practice

When doing calculations with thin lenses we use two, very familiar, equations:

The Thin Lens Equation:

and the magnification equation:

Sign conventions for thin lenses:

The focal length is positive for converging lenses and negative for diverging lenses.
The object distance is positive if the object is on the side of the lens from which the light is coming (this is usually the case, although when lenses are used in combination, it might not be so); otherwise, it is negative.
The image distance is positive if the image is on the opposite side of the lens from where the light is coming; if it is on the same side, d_i is negative. Equivalently, the image distance is positive for a real image and negative for a virtual image.
The height of the image, h_i, is positive if the image is upright, and negative if the image is inverted relative to the object. (h_o is always taken as positive).

Thin Lens Self-Assessment

Click here to access The Physics Classroom - Lens Practice. Answer questions: 24, 25, 28, 29, 33, 38, 45

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