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A concave mirror gives an image three ti...

A concave mirror gives an image three times as large as the object placed at a distance of 20 cm from it. For the image to be real, the focal length should be

A

10 cm

B

15 cm

C

20 cm

D

30 cm

Text Solution

Verified by Experts

The correct Answer is:
B
Magnification,
`m=(f)/(f-u)rArr -3=(f)/(f-(20))`
`rArr " "` The focal length of mirror, `f =-15 cm`
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MHTCET PREVIOUS YEAR PAPERS AND PRACTICE PAPERS-RAY OPTICS-EXERCISE 1 (TOPICAL PROBLEMS)
  1. An object of size 7.5 cm is placed in front of a convex mirror of radi...

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  2. The image formed by a convex mirror of focal length 30 cm. is a quarte...

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  3. A concave mirror gives an image three times as large as the object pla...

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  4. A point object is placed at a distance of 10 cm and its real image is ...

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  5. Object is placed 15 cm from a concave mirror of focal length 10 cm, th...

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  6. Where should a person stand straight from the pole of a convex mirror ...

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  7. Find the position of image from given diagram.

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  8. A plano convex lens is made of glass of refractive index 1.5. The radi...

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  9. At what distance from a convex lens of focal length 30cm an object sh...

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  10. A plano - convex lens is made of flint glass. Its focal length is

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  11. Distance of an object from a concave lens of focal length 20 cm is 40 ...

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  12. Where should an object be placed from a converging lens of focal lengt...

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  13. An object is placed at 10 cm from a lens and real image is formed with...

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  14. The real image which is exactly equal to the size of an object is to b...

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  15. A plano-convex lens of curvature of 30 cm and refractive index 1.5 pro...

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  16. The minimum distance between an object and its real image formed by a ...

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  17. A convex lens of refractive index 3/2 has a power of 2.5^(@). If it is...

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  18. Two thin lenses of focal lengths f(1) and f(2) are in contact. The fo...

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  19. Two thin lenses, one of focal length + 60 cm and the other of focal le...

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  20. A convex lens of focal length 40 cm is in contact with a concave lens ...

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