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# Need some help (light and sight) watch

1. An object is placed 10 cm in front of a lens, A; details of the image are given below. The process is repeated for a different lens, B.

Lens A real, inverted, magnified and at a great distance.

Lens B real, inverted and same size as the object.

Estimate the focal length of each lens and state whether it is converging or diverging.

Now I've figured that both lenses are converging as well as the focal length of lens B is 5 cm. But I couldn't get the focal length of the first lens, A.

Would you mind helping me figure it out?

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2. I don't see how you can give an exact answer here. Maybe they just want you to say wether it is larger or smaller than 5cm (or 10cm)?
3. (Original post by Darth_Narwhale)
I don't see how you can give an exact answer here. Maybe they just want you to say wether it is larger or smaller than 5cm (or 10cm)?
You make total sense. That is what I was pondering about. In the mark scheme, they just put 10 cm for the first one and 5 cm for the second (at the back of my reader, it might be incomplete perhaps?).

My answer would be: 5<f<10 for lens A, and 5>f for lens B.

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Updated: January 6, 2017
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