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Lens
Lens - SGH
Question | Answer |
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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 |