# Help plssssssss

#### lecker1003

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..)

question:

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...

#### berkeman

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?

#### lecker1003

i dont got a textbook.. we getting notes only.. and i dont have them.. i tried too google biut i dont find anything

#### berkeman

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.

#### lecker1003

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?

#### lecker1003

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

Gold Member

#### lecker1003

ok

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...

pls

and i have 4 more questions i dont know lol

#### lecker1003

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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