The Thin Lens Equation

1. The Thin Lens Equation Examples using lenses

2. A Converging/Convex Lens • In convex lenses, • f is positive • do is always positive • di can be positive or negative

3. A Diverging/Concave Lens • In concave lenses, • f is negative • do is always positive • di is negative

4. The Equation

5. Sample Problem • Calculate di

6. Sample Problem f = 17 cm do = 48 cm di = ?

7. Calculating Percent Error • You can check the accuracy of your drawings by comparing your measurements to your calculations. • Theoretical is the image distance you calculated using the thin lens equation • Experimental is the image distance you measured on your scale ray diagram • If you get a negative percent – just ignore the negative sign.

8. The Thin Lens Equation • The equation: • To use the thin lens equation, you need to follow this sign convention: • Object distances (do) are always positive • Image distance (di): • are positive for real image (image is opposite side of lens as object) • Are negative for virtual images (when the image is on the same side of the lens as object) • The focal length (f) is positive for converging lenses and negative for diverging lenses.

9. Practice • Complete Questions 4-11 on the Lenses Problem Set.