Focal length

JEE Advanced Tutorials › Optics questions › Focal length

A plano-convex lens has thickness of 4cm. when placed on a horizontal table with curved suface in contact with, the apparent depth of bottom most point of the lens is found to be 3cm. If the lens is inverted, the apparent depth of the centre of the plane place is 25/8cm. What is the focal length of the lens?

#Physics #Optics

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5 Answers

3

iitimcomin ·2009-07-17 18:26:56

first case apply refraction stuff...

Î¼/4 = 1/3//

secd case apply refraction across curved surface ,,,

Î¼1/v - Î¼2/u = Î¼1 - Î¼2 /R

find R,f from abv eqxns ...

then apply lens makers formula!!!!!!!!

(Î¼-1)(1/R1-1/R2) = 1/f

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1

injun joe ·2009-07-19 07:45:38

I have tried this. But the answer is not matching...Please post the answer so that I can check if it is right or not.

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3

iitimcomin ·2009-07-20 10:14:45

watz da ans. in da buk???????

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1

injun joe ·2009-07-25 07:23:54

-30cm
I'm getting -25 cm

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1357

Manish Shankar ·2009-07-25 08:10:13

I m also getting R as 25 cm and f as 75 cm

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