A thin biconvex lens of refractive index (3/2) and radius of curvature 30 cm is put in water (refractive index = (4/3) ). Its focal length is

Question

A thin biconvex lens of refractive index (3/2) and radius of curvature 30 cm is put in water (refractive index = (4/3) ). Its focal length is (A) 0.15 m (B) 0.30m (C) 0.45m (D) 1.20m

Tardigrade Admin · Accepted Answer

Using lens-makers formula (1/ mathrmf)=((μ1/μ2)-1)((1/ mathrmR1)-(1/ mathrmR2)) (1/ mathrmf)=((3 / 2/4 / 3)-1)((1/0.3)+(1/0.3)) Or (1/f)=((9/8)-1)((2/0.3)) Or (1/f)=(1/8)× (2/0 .3) or f=1.20 m

Q. A thin biconvex lens of refractive index $\frac{3}{2}$ and radius of curvature $30 c m$ is put in water (refractive index = $\frac{4}{3}$ ). Its focal length is

$0.15 m$

$0.30 m$

$0.45 m$

$1.20 m$

Using lens-makers formula
$\frac{1}{f} = (\frac{μ _{1}}{μ _{2}} - 1) (\frac{1}{R _{1}} - \frac{1}{R _{2}})$
$\frac{1}{f} = (\frac{3/2}{4/3} - 1) (\frac{1}{0.3} + \frac{1}{0.3})$
Or $\frac{1}{f} = (\frac{9}{8} - 1) (\frac{2}{0.3})$
Or $\frac{1}{f} = \frac{1}{8} \times \frac{2}{0.3}$ or $f = 1.20 m$

Q. A thin biconvex lens of refractive index 23​ and radius of curvature 30cm is put in water (refractive index = 34​ ). Its focal length is

0.15m

0.30m

0.45m

1.20m

Using lens-makers formula f1​=(μ2​μ1​​−1)(R1​1​−R2​1​) f1​=(4/33/2​−1)(0.31​+0.31​) Or f1​=(89​−1)(0.32​) Or f1​=81​×0.32​ or f=1.20m

Q. A thin biconvex lens of refractive index $\frac{3}{2}$ and radius of curvature $30 c m$ is put in water (refractive index = $\frac{4}{3}$ ). Its focal length is

$0.15 m$

$0.30 m$

$0.45 m$

$1.20 m$