a biconvex lens of glass of refractive index 1.5 having focal length 20cm is placed in a medium of refractive index 1.65. find its focal length
Answers
Answered by
28
n₁ = index of refraction of glass of lens = 1.5
n₂ = index of refraction of medium = 1.65
R = radius of curvature biconvex lens = 20 cm
f = focal length of the glass of lens = ?
focal length for biconvex lens is given as
1/f = ((n₁/n₂) - 1) (2/R)
inserting the values in the above equation
1/f = ((1.5/1.65) - 1) (2/20)
1/f = ((1.5/1.65) - 1) (1/10)
f = -110 cm
hence the focal length of the biconvex lens is -110 cm
Answered by
2
Answer:
Explanation:
From LMF,
f
1
=(n−1)(
R
1
1
−
R
2
1
)
Since it is diverging , f=−24cm
Given that R
1
=2R
2
,n=1.5
−24
1
=(1.5−1)(
2R
2
1
−
R
2
1
)
−12
1
=
2R
2
−1
R
2
=6cm,R
1
=12cm
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