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Ask iit jee aieee pet cbse icse state board community Community Discussion Question: conceptuals !!!!
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[Post New]30 Nov 2007 21:17:46 IST
    Subject: conceptuals !!!!
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ashgirl (1434)

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Q1 the radii of curvature of both the surfaces of a lens are equal. if one of the surfaces is made plane, by grounding, how will the focal length change??
 i know the ans but i dont know how to arrive at it.
ans is twice
 
Q2. a lens of glass is immersed in water. how is power of lens affected?
ans power will decrease. (HOW???)
 
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[Post New]30 Nov 2007 22:02:29 IST
    Subject: Re:conceptuals !!!!
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lokeshsardana (685)

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See both of ur questions are based on lens maker formula......which is
 
1/f = (u2/u1- 1)(1/R1-1/R2)........
 
where u2 and u1 are refractive indices of material of lens and surrounding medium resp.
 
now in first problem as one surface is flattened..so, u can take one of  its radius as infinity..........put in formula to get result..................
 
in second one, as surrounding medium is water so.u1> 1 and also power =1/f .............so, power in water decreases as compared to air..
 
 
satisfied!!!!!!!!
LOKESH SARDANA,
department of Production and Industrial engineering,
Indian Institute of Technology,Roorkee.


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[Post New]30 Nov 2007 23:22:17 IST
    Subject: Re:conceptuals !!!!
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harsh15 (222)

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the answer is correct ,whenever lens is dipped in a medium having lesser refractive index then the focal length of the lens will increase resulting in the decrease in the power.
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[Post New]30 Nov 2007 23:24:31 IST
    Subject: Re:conceptuals !!!!
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shevchenko (88)

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sorry.this shud not be here.can someone get the link for il finar ebook.will surely rate.
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