Beck-1Physics 224 Thin Lens and Image FormationJulie BeckLab Partners: Hannah D., Mallory C., Yashvi P.Date Performed: November 17, 2015

Beck-2Objective:The objective of this lab was to measure the focal length of thin lens and to use thin lens to form images and study the thin-lens equation. The chromatic aberration of thin lens was also observed during this lab.Introduction/Background:Optics utilizes a diverse set of lenses for image formation and spectroscopic measurement. In this lab, the combinations of converging and diverging lenses were used to observe diffraction and image formation. The thin lenses used were two bi-convex lenses (converging) and a convex-concave lens (diverging).The thin lens equation, 1/p + 1/q = 1/f, can be used to describe the image formed by diffraction through the thin lens. (p) is the object distance, it is the distance between the object and the center of the lens, (q) is the image distance, which is the distance between the image and the center of the lens, and (f) is the focal length. q is positive for a real image and negative for a virtual image. The magnification of the image can be determined by the equation M = image height / object height = (–q/p). Image height is positive for an upright image and negative for an inverted image.Thin lenses can be placed together so that their principal axes coincide (parallel) and are in contact so the can behave like a new thin lens. The compound focal length for this situation can be calculated using the equation 1/f1+ 1/f2= 1/f. The focal length of a bi-convex thin lens follows the lens-maker’s equation, 1/f = (n-1)(1/R1+ 1/R2). (n) is the refractive index of the lens, (R1)is the radius of the curvature of its front surface and (R2)is the radius of the curvature of its back surface. The refractive index is different at different wavelengths, so the focal length will vary with varying wavelengths. This means that with differing n values for different color lenses,the focal length will differ, as explored in the second part of this experiment. The focal length forred light is longer than the focal length for blue light. This leads to chromatic aberration for the lens.Procedure:First, the object height was measured. A calibrator was used to measure the object height, h. This value was 4.2 cm and was recorded in Table 1.