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Focal length calculation and graph Q 
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#1
Jun707, 09:46 AM

#2
Jun707, 09:52 AM

P: 92

use similar triangles to proove that the formula for a lens is (1/U + 1/V = 1/f)
or u can find it anywhere on the internet. it is a very easy proof, won't take you 5 min. therefore it is 1/U and 1/V not U and V 


#3
Jun707, 10:24 AM

P: 38

not entirly sure what you mean, triangles?
anyway, that 1/V vs 1/U graph with my experimental results is proof that the equation is true. im just asked why the U and V graph doesnt give an accurate value for the focal length? 


#4
Jun707, 11:31 AM

P: 92

Focal length calculation and graph Q
ok
if you draw your object, lens and image on a piece of paper with two of the rays you use to draw a ray diagram, you can see that there are some similar triangles on that figure. Try using similar triangles and getting two equations involving U, V and f. then solve them simultaneously to get "1/U + 1/V = 1/f " (if you cannot I can give you the solution but try it first :) U and V graph cannot give you an accurate value for the focal length because the relation between the two is not related to f in any simple way. if u play around with the equation I gave you above you might get " "[(v+U)/U]*f=V" but this won't make it any easier. perhaps the answer to your question is that the nature of lenses does not provide us with that simple relations where you plot U versus V and get a slope or a y intercept of f 


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