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A concave lens is placed in the path of convergent rays. The rays are focussed on the axis 15 cm behind the lens. Where would these rays have been focussed in the absence of the lens ? Focal length of the lens is 30 cm.

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The correct Answer is:
At a distance of 10 cm behind the lens
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SL ARORA-RAY OPTICS-Problems For Self Practice
  1. The distance between a convex lens and a plane mirror is 15 cm. The pa...

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  2. A concave lens focal length 10 cm is placed on the axis of concave mir...

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  3. A concave lens is placed in the path of convergent rays. The rays are ...

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  4. A needle 10 cm long is placed along the axis of a convex lens of focal...

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  5. When a slide is placed 15 cm behind the lens in a projector, an image ...

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  6. In the diagram shows below rays are coming from infinity and after pas...

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  7. In the following ray diagram are given the position of an object O, im...

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  8. In the following diagram are shown the position of an object O, image ...

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  9. A compound lens has been formed by joinined a convex and a concave len...

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  10. Two thin lenses of power + 3 D and - 1 D are held contact with each ot...

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  11. A what distance must an object be placed from convex lens of power 4D ...

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  12. Find the focal length and power of a convex lens, which when placed in...

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  13. The power of a thin convex lens of glass is 5 dioptre. When it is imme...

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  14. A concave lens is kept in contact with a convex lens of focal length 2...

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  15. A compound lens is made of two lenses having powers +15.5 D and -5.5D....

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  16. Ray coming from an object situated at infinity, fall on a convex lens ...

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  17. A ray of light is incident at an angle of 60^(@) on one face of a pris...

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  18. The refracting angle of a glass prism is 60^(@). The value of minium d...

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  19. The refractive index of the material of a prism of 60^(@) angle for ye...

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  20. A ray of light incident at 49^(@) on the face of an equilateral prism ...

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