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प्रश्न
The above image shows a thin lens with a focal length of 5m.
- What is the kind of lens shown in the above figure?
- If a real inverted image is to be formed by this lens at a distance of 7m from the optical centre, then show with calculation where should the object be placed.
- Draw a neatly labelled diagram of the image formation mentioned in (ii).
उत्तर
- Convex lens
- `1/f = 1/v - 1/u`
In this case, v = 7m and f = 5m
Putting the values in the equation, we get,
`1/5 = 1/7 - 1/u`
`1/u = 1/7 - 1/5 = (5 - 7)/35 = (-2)/35`
`u = -35/2 = -17.5` m
The object will be placed 17.5 m on the left of the convex lens. 
(two rays, arrows, and object placed beyond 2f on the left)
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