Physics 109 1nd Edition Lecture 4 Outline of Last Lecture I Refraction Review a Snell s Law b Critical Angle II The prism III Converging Lens a Lens formula b 3 easy rays c Magnification Outline of Current Lecture I Diverging lens a 3 easy rays b Lens Formula II Dispersion Current Lecture I Diverging lens are thinner in the middle so they deflect light rays away from the axis a The image of a diverging lens is always i Virtual ii Right side up iii In front of lens iv Smaller than object b 3 easy rays i The first ray goes straight through the center of the lens ii The second ray is parallel to the optical axis This ray is deflected out of the lens and appears as if it came from the focal point on the same side as the object iii The third ray is the ray from the top of the object heading in the direction of the focal point on the opposite side of the lens with respect to the object This ray will come out parallel to the axis seeming to come from the point already identified by the first two rays These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute This image shows the 3 easy rays for a diverging lens The image is virtual and upright II c Lens Formula i The lens formula tells you how object distance o and image distance i are related to the focal length f of a lens 1 O is the length from the object to the lens 2 i is the length from the lens to the image 3 f is the length from the lens to the focal point a The focal length of a diverting lens is stated as a negative because the image is in front of the lens ii The equation is 1 i 1 f 1 0 1 Example Focal length 10 cm object is 10cm from lens Where is the image 1 i 1 10 1 10 2 10 1 5 i 5cm so the image is 5 cm from the lens on the same side of the lens Dispersion a The index of refraction is different for different colors i Red is a primary color because it is very difficult to kink blue kinks easily