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An object is 5 m to the left of a flat screen. A converging lens for which the focal length is 0.8m is placed between object and screen.Show that for two positions of lens form images on the screen and determine how far these positions are from the object? |
Answer» SOLUTION :Usingthe lensformula`(1)/(V) -(1)/(u) =(1)/(F)`  we have`(1)/(5-u) +(1)/(u )=(1 )/(0.8) or (1)/(5-u) +(1)/(u) =1.25` ` thereforeu+5 -u =1.25u(5-u) or 1.25u^2 -6.25u + 5=0` u= 4mand 1m Both the values are real, which MEANS there exist two POSITIONS of lens that form images of object on the SCREEN. |
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