A convexo-concave lens has faces of radii 3 and 4 cm respectively, and is made of glass of refractive index 1.6, its focal length is

Question

A convexo-concave lens has faces of radii 3 and 4 cm respectively, and is made of glass of refractive index 1.6, its focal length is (A) 40 cm (B) -40 cm (C) 20 cm (D) -20 cm

Tardigrade Admin · Accepted Answer

(1/f)=(n-1) [(1/R1)-(1/R2)]=(1.6 -2 ) [ (1/-3)-(1/4)] Both R1 and R2 have same sign.

Q. A convexo-concave lens has faces of radii 3 and 4 cm respectively, and is made of glass of refractive index 1.6, its focal length is

40 cm

-40 cm

20 cm

-20 cm

$\frac{1}{f} = (n - 1) [\frac{1}{R _{1}} - \frac{1}{R _{2}}] = (1.6 - 2) [\frac{1}{- 3} - \frac{1}{4}]$
Both $R_{1} an d R_{2}$ have same sign.

Q. A convexo-concave lens has faces of radii 3 and 4 cm respectively, and is made of glass of refractive index 1.6, its focal length is

40 cm

-40 cm

20 cm

-20 cm

f1​=(n−1)[R1​1​−R2​1​]=(1.6−2)[−31​−41​] Both R1​andR2​ have same sign.

$\frac{1}{f} = (n - 1) [\frac{1}{R _{1}} - \frac{1}{R _{2}}] = (1.6 - 2) [\frac{1}{- 3} - \frac{1}{4}]$
Both $R_{1} an d R_{2}$ have same sign.