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Lens - SGH

Define power for a lens? Power=1/focal length
What is the unit for power of a lens? Dioptre, D
What is the lens formula? 1/f = 1/u + 1/v
What kind of image is formed from a converging lens, when the object-to-lens distance is smaller than the focal length? Virtual image
What are the differences between a real and virtual image? A real image is inverted and can be formed on a screen, whereas virtual images are upright and cannot be formed on a screen.
For a converging lens, where must the object be placed to give a real image of the same size as the object? At u=2f because using: 1/f = 1/u + 1/v when object-size=image-size, u must equal v so you get 1/f = 1/u + 1/u = 2/u therefore u = 2f
Created by: sandeep15