A converging lens of unknown focal length is mounted on an optics bench
PHYSICS · Multi-part · CBSE · Physics · Ray Optics and Optical Instruments · Ray Optics and Optical Instruments
Problem
A converging lens of unknown focal length is mounted on an optics bench. An object is placed 18cm to the left of the lens, and a sharp, inverted image appears 9.0cm to the right of the lens.
(a) Without performing any calculations, draw a scaled ray diagram that predicts the approximate position of the image relative to the lens and indicates whether the image is real or virtual. Explain the features of your diagram that lead to this prediction.
(b) Calculate the focal length of the lens from the given object and image distances. Include the appropriate algebraic sign and units in your answer.
(c) Your diagram in part (a) and your calculation in part (b) do not yield exactly the same focal length. Identify two reasonable sources of discrepancy between the graphical and numerical methods and explain how each source could affect the result.
(d) The object is now moved so that it is 30cm from the lens. Predict qualitatively, before calculating, whether the image will be larger or smaller than the object and whether it will still be real. Then compute the new image distance and magnification to verify your prediction.