| Question |
 |
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| 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
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Buen Viaje lv.2 ch 8
