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the focal length of a plano-concave lens is -10cm, then its focal length when its plane surface is polished is?

the focal length of a plano-concave lens is -10cm, then its focal length when its plane surface is polished is?

Grade:12

3 Answers

Nirmal Singh.
askIITians Faculty 44 Points
8 years ago
When Plane surface is polished then it bahave like a concave mirror and it focal length will be - 10 cm

Regards,
NIrmal Singh
Askiitians Faculty
vaanya
18 Points
8 years ago
the answer is +5cm. plz tell me how to solve it.
Kajal
15 Points
4 years ago
Any lens + plane mirror = -1/2 (f)
=-1/2 (-10)
=+5 
=Ans
its ans shortcut by our physics teacher , don't tell him that i have leaked this awesome shortcut!! :)

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