In the figure, an air lens of radii of curvature 10 cm (R1=R2=10 cm ) is cut in a cylinder of glass (μ=1.5). The focal length and the nature of the lens is

Question

In the figure, an air lens of radii of curvature 10 cm (R1=R2=10 cm ) is cut in a cylinder of glass (μ=1.5). The focal length and the nature of the lens is (A) 15 cm, concave (B) 15 cm, convex (C) ∞, neither concave nor convex (D) 0 , concave

Tardigrade Admin · Accepted Answer

(1/f)=( g μa-1)((1/R1)-(1/R2)) =((2/3)-1)((2/10)) ⇒ f=-15 cm, so behaves as concave lens.

Q. In the figure, an air lens of radii of curvature $10 c m$ $(R_{1} = R_{2} = 10 c m)$ is cut in a cylinder of glass $(μ = 1.5)$ . The focal length and the nature of the lens is

15 cm, concave

15 cm, convex

$\infty$ , neither concave nor convex

0 , concave

$\frac{1}{f} = (_{g} μ_{a} - 1) (\frac{1}{R _{1}} - \frac{1}{R _{2}})$
$= (\frac{2}{3} - 1) (\frac{2}{10})$
$\Rightarrow f = - 15 c m$ , so behaves as concave lens.

Q. In the figure, an air lens of radii of curvature 10cm (R1​=R2​=10cm) is cut in a cylinder of glass (μ=1.5). The focal length and the nature of the lens is