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Help plssssssss

  1. Dec 8, 2006 #1
    hi, i got a real problem. i have a question here and have absolut no clue what i have to do and which equation i have to use...

    ( for my shame, i was sick at that time we done it in school..)


    A diver is at the bottom of a lake, which is 10m deep. if he looks straight up he sees the sky, but if he looks at the surface of the water a little further away he sees a reflection of the lake-bed in the calm surface. calculate the distance from his position to the nearest point on the bed that he can see clearly in the reflection. take the refraktive index of the water as 1.33, and of the air as 1.

    i really was thinking about it, but i have no clue what i have to do...
  2. jcsd
  3. Dec 8, 2006 #2


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    Staff: Mentor

    What can you tell us about "total internal reflection"? Your textbook will have introduced this concept before asking you that question. Or you can just google that expression, or check wikipedia.org. Now can you show us how you calculate that angle in the problem?
  4. Dec 8, 2006 #3
    i dont got a textbook.. we getting notes only.. and i dont have them.. i tried too google biut i dont find anything
  5. Dec 8, 2006 #4


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    Staff: Mentor

    Go to www.wikipedia.org, and do the search on Total Internal Reflection. Tell us what you find out about the "critical angle". Now you're good to go! Be sure to show your work.
  6. Dec 9, 2006 #5
    other prob

    so, i have another prob too:

    i tried to calculate b:

    a. Draw a diagram to show a convex lens of focal length 10cm being used as a simple microscope( magnifying glass) producing an image at the distance of distinct vision -- erledigt!

    b. what is the angular magnification of this arrangement?

    c. what would be the angular magnification be if the image were infinity?

    i got m= d/f = 25/10 = 2.5

    can that be right?
  7. Dec 9, 2006 #6
    also i just looked in wikipedia with:

    Total Internal Reflection and critical angle.. but it dont help me at all..

    i dont understand the prinzip
  8. Dec 9, 2006 #7


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    Gold Member

  9. Dec 9, 2006 #8

    also i understand the basic now.. the picture. but i dont know really what i have to calculate..

    i know 10m to the surface when he looks straight up. what is 90 degree with the bottem

    the next i know is the tir should be 48.6 degree.. thats the maxc or its not anymore refracting..

    but know i stock and i discussed it with a friend and nearly he shoot me...

    3hrs long and still no clue...


    and i have 4 more questions i dont know lol
  10. Dec 10, 2006 #9
    ok i got it now.. but now i got next problem

    float(2*10*tan(arcsin(1/1.33))) = 22.80841284

    this one:

    a compound microscope is made using a 2cm focal length lens as objectiv an a 10cm focal lenth lens an a eyepiece. the lenses are sepeerated by 30cm, and the final image is viewed at the distance of dinstinct vision

    question: calculate distance between object and first lense
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