JEE MainPhysicsGeometrical OpticsMCQ+4 / −1
For a concave lens of focal length f, the relation between object and image distances u and v, respectively, from its pole can best be represented by (u = v is the reference line) :
- A

- B

- C

- D

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Correct answer: D
- Use the lens formula
For a thin lens,
For a concave lens, the focal length is negative. Let its magnitude be , so actual focal length is . Hence,
- Rearrange to get relation between and
Multiply by :
So,
This is the required relation between and .
- Nature of image for a concave lens
For a real object placed to the left of a concave lens:
- image is virtual and on the same side, so
Thus the physically relevant curve lies in the third quadrant of the - plane.
- Check asymptotic/limiting behavior
From
we get
Now examine limits:
- As ,
- As ,
So the graph starts near the origin in the third quadrant and approaches the horizontal line as .
- Compare with the reference line
For a concave lens, the image always lies between optical center and focus, so Since both and are negative, this means Therefore the curve lies above the line in the third quadrant.
- Hence the correct graph
The correct option must show:
- branch in the third quadrant,
- passing near the origin,
- lying above the line ,
- approaching for large negative .
This corresponds to Option D.
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