A lens is an object with some shape ([[Convex]] or [[Concave]]) such that the materials [[Index of Refraction]] $\eta$ is different than that of airs. This is used to bend light coming at different angles to manipulate it in some way (for example, focus it on a point). ![[Lens .excalidraw.svg|500]] %%[[Lens .excalidraw.md|🖋 Edit in Excalidraw]]%% >[!tip] Important note on the [[Sign|sign]] of [[Distance|distances]] >Object distances on the left of the mirror (side of the incident wave) are positive when they appear on the left, and image distances on the right of lens are positive. However, the [[Focal Point|Focal Length]] is negative to the left and positive to the right >![[Pasted image 20251121131436.png|invert_B|500]] ### Lens Equation $\huge \frac{1}{f} = \frac{1}{d_{O}} + \frac{1}{d_{I}} $ This is similar to the [[Spherical Mirror|Spherical Mirror Equation]], but the notion of $d_O$ and $d_Is signs are flipped. >[!multi-column] >>[!example] [[Concave]] Lens >>![[Lens _0.excalidraw.svg|500]] >>%%[[Lens _0.excalidraw.md|🖋 Edit in Excalidraw]]%% > >>[!example] [[Convex]] Lens >>![[Lens .excalidraw.svg|500]] >>%%[[Lens .excalidraw.md|🖋 Edit in Excalidraw]]%% $\huge \frac{1}{f} = (\eta-1)\left( \frac{1}{r_{1}} + \frac{1}{r_{2}} \right) $