Refraction Of Light

Speed of light is maximum in Water.

The refractive indices of any medium are inversely proportional to the speed of light in it. We can see from the formula of refractive indices:

Speed _glass = =

Similarly, for,

Speed _glycerine =

Speed _{sunflower oil} =

Speed _water =

Speed _{Flint glass} =

Here we see that,

Speed _water > Speed _glycerine > Speed _glass > Speed _{Flint glass} > Speed _{sunflower oil}

We can also say that greater the refractive indices lesser will be speed.

i. Convex lens will form erect and magnified virtual image.

Diagram of convex lens when object is place between the focus F and optical centre C.

Here object is AB and its virtual image is A^’B^’. Image height is greater than object size (magnified) and image is upright (erect).

ii) Concave lens will form erect and diminished virtual image.

Diagram of concave lens when object is place between the infinity and optical centre C.

Here object is AB and its virtual image is A^’B^’. Image height is less than object size (diminished) and image is upright (erect).

When the object is placed at 2F in convex lens its image will be same size as the object. Here is the ray diagram:

a) MN is convex lens

As after refraction by the lens (MN) ray converge to focus (F), this only happen with convex lens (converging lens).

b) Image will be larger than object (enlarged), can be taken on the screen (Real) and upside down (inverted).

c) Ray diagram :

Object – OB

Image – O’B’

Image is Enlarged, Real and inverted.

Power term related to focal length of a lens. The reciprocal of the focal length of a lens in metres is called the power of the lens.

Its is a capacity of a lens to bend the rays of light. The smaller the focal length, the greater is the bending of a ray of light and vice- versa.

SI unit of power is diopter represented by D

Given:

concave lens of focal length =25 cm

From the formula of power,

Here focal length of concave length is taken as negative.

Therefore concave lens of focal length =

Power of concave lens is: - 4 D

(a) Medium 1 has greater optical density .

(b) In both the diagram ray is coming from the same medium i.e. air also angle of incident is same. In first case angle of refraction is 20⁰ and in diagram 2^nd angle of refraction is 30⁰ so derivation of light is more in medium 1 than in medium 2.So more the derivation of light greater the optical density.

(c) Medium 1 has greater index than medium 2.

Optical density of a medium 1 is greater than medium 2 so the speed of light in medium 1 will be slower than the speed of light in medium 2. Slower the speed indicates more the value of refractive index.

Many students get confused in optical density and physical density here optical density mean how fast or how slow light propagates through a medium where as physical density means how much lighter or heavier the object is when measuring with respect to water.

Given-

Lens using: convex

The height of object: 3cm

The focal length of lens: 10cm

The object is placed at 15 cm from the optical center

The formula of the lens:

So, let suppose image is formed at a distance of v cm from the optical center

Ray diagram will look something like this:

Here (from sign convention direction of incident light is left to right)

AB = object = +3cm (upward direction from x-axis)

CF = focal length = 10 cm (direction is C to F (right side) i.e. left to right same as direction of incident light)

CB = u = - 15 cm (direction is C to B i.e. right to left opposite to incident light direction)

So, let the distance of image will be v cm,

So

Here we see that v is positive so image will be formed in right side of lens (C’B’)

Nature of the image is real (can be taken on a screen) , inverted (upside down)and Enlarged (large than object size) .

From the formula of magnification

So, Height of image (h_i) = Height of object (h_o)

Here height of object h_o is: + 3 cm

Height of image (h_i) =

Height of image (h_i) =

A prism is a transparent triangular piece of glass. It consists with plane (flat) refracting sides, an apex (top point) and a base (bottom). A ray of light incident to a prism is always bent towards the base of the prism. Here is light from the object bend toward the base of prism (AB).

So let consider two prisms placed base to base. Light rays through them coverage (come together) at some point on the other side of the prism. Look here -

In most of the cases, curved surface lenses are spherical (part of a sphere) and such lenses are called spherical lenses. This type of lens is also called plus lens.

Here is a complete ray diagram of two prism

We assume incident light 1 and 2 are coming from infinity so in the diagram both the ray was seen to convergent at a particular point. This is same as in convex lens i.e. when a ray of light from infinity strike to the lens converge at a point called focus. The same thing is happening here also so when these two prisms joint together and made thinner then this will act as a convex lens.

**Additional Information**:

To make concave lens we have to join two prisms from its apex.

Look here:-

As when incident ray falls to one of the side of prism it bend toward the base of a prism, making light to diverge (spread apart) on the other side of the prism. This type of lens is also called minus lens.