(i) When ray of light enters from air medium into water, medium it bends towards the normal as shown.

(ii) When ray of light enters from water medium into air medium, it bends away from the normal as shown

\(P=\frac { 1 }{ f } \)
For obtaining more convergent light, power of lens must be larger. Therefore, its focal length must be smaller. Therefore, the lens of f = 20 cm will provide more convergent light.

Yes, a convex lens of focal length 20 cm can produce a magnified virtual as well as real image. The statement is correct. For magnified virtual image, the object must be held at a distance less than 20 cm from the lens. For magnified real image, the object must be held at a distance between 20 cm and 40 cm from the lens.

(a) Image found is enlarged and behind in case of concave mirror.
(b) Image formed is enlarged and on the same side as the object in the case of convex lens.
(c) Image found is diminished and between focus and optical centre on the same side as the object in case of concave lens.
(d) Image formed is diminished and between pole and focus, behind it in case of a convex mirror.

The focal length of a lens depends on
(a) Radii of curvature of the surface of the lens.
(b) Nature of material of the lens.
(c) Nature of medium in which lens is placed.

The rough focal length of a convex lens is obtained by forming sharp image of a very distant object on a screen. The distance of the screen from the lens gives us the rough focal length of the lens.
This method is not applicable to a concave lens, as image formed by a concave lens is virtual and it cannot be taken on the screen.

One dioptre is the SI unit of power of lens, whose focal length is 1 m.

Refractive index of any medium w.r.t. another indicates the extent to which light bends when it enters from first medium to the given medium. The given value of refractive index also states that speed of light in diamond is 1/2.42 times to the speed of light in vacuum.

The field of view of a convex mirror is wider than that of concave mirror and convex mirror always produces erect image of object, so we prefer convex mirror as rear view mirror for vehicles.

The principal focus of a concave mirror is a point on the principal axis at which a light ray parallel to the principal axis converges after reflection.
Light rays that are parallel to the principal axis of a concave mirror converge at a specific point on its principal axis after reflecting from the mirror. This point is known as the principal focus of the concave mirror.
It is denoted by F.
 

Given, radius of curvature, R = 32 cm
As we know, focal length, \(f=\frac{radius \quad of \quad curvature}{2}\)
So, \(f=\frac{32}{2}=16 \quad cm\)

Object distance, u = -25 cm, Object height, h = 5 cm, Focal length, f = +10 cm Substituting the values in the lens formula,
\(\frac { 1 }{ u } +\frac { 1 }{ v } =\frac { 1 }{ f } \)
We get v = 16.66 cm
The positive value of v shows that the image is formed at the other side of the lens.
Magnification =\(\frac { h' }{ h } =-\frac { v }{ u } \) =-16.66/25=-0.66
The negative sign shows that the image is real and formed behind the lens.
Magnification m=\(\frac { h' }{ h } \)
h' =-3.3 cm
The negative value of image height indicates that the image formed is inverted. The position, size, and nature of image are shown in the following ray diagram.