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Virtual Image-

• The image obtained when light rays are not really meeting but appears to meet only, is called a virtual image.
• In general, real images are located in front of a mirror while virtual images behind the mirror
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• In a ¹onvex mirror irrespective of the position of the object, the image formed is always virtual, erect but diminished in size

They form both Real and virtual image

 When the concave mirror is placed very close to the object, a virtual and magnified image is obtained

When there is increase in the distance between the object and the mirror, the size of the image reduces and real images are formed

Magnification-

It is the ratio of the size of the image to that of the object

Uses of Concave and convex mirror-

Concave mirrors are used in or as-

In headlight of a car or in torchlight to get wider parallel beam of lights

In Telescope to collect light from distance source

Shop security mirror or traffic security mirror

In cosmetic mirror to produce enlarged image

Used by dentists to see teeth and other areas in the mouth

Use of convex mirror-

They are placed near ATMs so that bank customers can check if someone is behind them

They are widely used as rear-view mirrors in automobiles and vehicles

Refraction of Light-

The deviation of light rays from its path when it travells from one transparent medium to another transparent medium, is called refraction of light

Refractive index : The refractive index of a medium is given by ratio of velocity of light in vacuum to that of velocity of light in medium

 velocity of light in vacuum / velocity of light in medium = c/v

Laws of Refraction-

(i) The incident ray, the refracted ray and the normal at the point of incidence, all three lies in the same plane.

(ii) The ratio of sine of angle of incidence to the sine of angle of refraction is constant for a pair of two media

Converging or Convex Lens-

The lens in which light rays that enter it parallel to its axis cross one another at a single point on the opposite side with a converging effect is called converging lens.

This lens is  thicker at the centre and thinner at its end is called convex lens

Concave Lens or Diverging lens-

A lens which is thicker at edges and thinner at middle, is called a concave or diverging lens

Images formed by Convex lens-

When an object is placed at infinity, the real and highly diminished image is formed at the focus

When an object is placed beyond the centre of curvature, the real image with less size is formed between the centre of curvature and focus

When an object is at the centre of curvature, the real image of same size is formed at the other centre of curvature

When an object is placed in between the centre of curvature and focus, the real image with larger size than object is formed behind the centre of curvature

When an object is placed at the focus, a real image is formed at infinity with very large size

When an object is placed in between focus and optical centre, a virtual image is formed. The size of the image is larger than that of the object

Images formed by concave lens-

When an object is placed at a finite distance from the lens, a virtual image is formed between the optical centre and the focus of the convex lens. The size of the image is smaller than that of the object

When an object is placed at infinity, a virtual image with highly dimished size is formed at the focus

Power of Lens -

The ability of a lens to converge or diverge the rays of light incident on it is called the power of the lens

The power of a convex (converging) lens is positive and for a concave (diverging) lens it is negative

SI unit of power is diopter (D)

Total internal reflection-

Total internal reflection occurs when a light ray is completely reflected at the boundary between two media of different densities or

When a ray of light travelling from denser medium to rarer medium is incident at the interface of two medium at an angle greater than the critical angle for the two media, the ray is totally reflected back to denser medium

 It occurs only when angle of incidence in denser medium is greater than critical angle

The angle of incidence in the denser medium at which the refracted ray just grazes the surface of separation is called the critical angle c of the denser medium

Application-

Brilliance of diamonds is due to Total Internal Reflection

Total internal reflection is used in optical fibre communication(An optical fibre is a very thin fibre made of glass or quartz having radius of the order of micrometer)

Mirage-

In deserts the air that is present near the ground sometimes gets hotter as compared to the other place above it.

The dot air is less dense as comparison to cold air and have less refractive index

The cold air has a large refractive index and is denser.

Thus, with the increase in height, the optical density also increases and vice versa.

When a beam of light passes through a longer object, the light bends away from the normal and undergoes total internal reflection

Due to this the actual position of object is perceived differently by the observer

Other application includes-

Used on medical fiekld like endoscopy etc.

Data transmission etc.

Prism-

 A prism is a transparent medium bounded by the three plane faces. Out of the three faces, one is grounded and the other two are polished. The polished faces are called refracting faces

Dispersion of Light-

The splitting of white light into its constituent colours in the sequence of VIBGYOR((Violet,Indigo, Blue, Green,Yellow, Orange and Red) , on passing through a prism is called dispersion of light.

There is maximum dispersion or deviation in case of violet colour and lowest in case of Red colour

Formation of Rainbow-

It is formed due to fo

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