Beck-1Physics 224Thin 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 lensto form images and study the thin-lens equation. The chromatic aberration of thin lens was alsoobserved during this lab.Introduction/Background:Optics utilizes a diverse set of lenses for image formation and spectroscopicmeasurement. In this lab, the combinations of converging and diverging lenses were used toobserve 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 bydiffraction through the thin lens. (p) is the object distance, it is the distance between the objectand the center of the lens, (q) is the image distance, which is the distance between the image andthe center of the lens, and (f) is the focal length. q is positive for a real image and negative for avirtual image. The magnification of the image can be determined by the equation M = imageheight / object height = (–q/p). Image height is positive for an upright image and negative for aninverted image.Thin lenses can be placed together so that their principal axes coincide (parallel) and arein contact so the can behave like a new thin lens. The compound focal length for this situationcan be calculated using the equation 1/f1+ 1/f2= 1/f. The focal length of a bi-convex thin lensfollows 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 itsback surface. The refractive index is different at different wavelengths, so the focal length willvary 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 thelens.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.

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