Question

A double convex lens has two surfaces of equal radii 'R' and the focal length of the lens is half the radius of the curvature . Find the refractive index

Answer 1

refractive index of double convex lens is 2.

A double convex lens has two surfaces of equal radii 'R' and the focal length of the lens is half the radius of the curvature

using formula, 1/f = (μ - 1)[1/R1 - 1/R2]

here, R1 = R , R2 = -R and f = R/2

so, 1/(R/2) = (μ - 1)[1/R + 1/R]

⇒2/R = (μ - 1)(2/R)

⇒1 = μ - 1

⇒μ = 2

hence, refractive index of double convex lens is 2.

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Answer 2

$\huge\bold\purple{Answer:-}$

1/f=(n-1)(1/R1+1/R2)

n=1.5

R1=R2=R

1/f=(1.5-1)(1/R+1/R)

1/f=(0.5)(1+1/R)

1/f=1/2(2/R)

1/f=1/R

f=R