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  • Confused! kindly explain, A concave mirror of focal length 'f1' is placed at a distance of 'd' from a convex lens of focal length 'f2'. A beam of light coming from infinity and falling on this convex lens - concave mirror comb

A concave mirror of focal length 'f1' is placed at a distance of 'd' from a convex lens of focal length 'f2'. A beam of light coming from infinity and falling on this convex lens - concave mirror combination returns to infinity. The distance 'd' must equal:

  • Option 1)

    f1+f2

  • Option 2)

    -f1+f2

  • Option 3)

    2f1+f2

  • Option 4)

    -2f1+f2

 

Answers (1)

best_answer

First image will form at distance f_{2} from lens.

For final image to return to infinity, the first image must be centre of curvature of mirror. Hence distance of image I from the mirror must be equal to 2f_{1}

\therefore d=2f_{1}+f_{2}


Option 1)

f1+f2

This option is incorrect.

Option 2)

-f1+f2

This option is incorrect.

Option 3)

2f1+f2

This option is correct.

Option 4)

-2f1+f2

This option is incorrect.

Posted by

Aadil

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