Param Himalaya - परम हिमालय

The image is formed at that point where at least two refracted light rays meet ( or appear to meet ) . Rules for convex lens :  1. Light ray incident parallel to the principal axis , meet at focus.  2. Light ray incident from focus , become parallel to the principal axis after Refraction.  3. Light ray incident on the pole of the lens passes without any deviation. Formation of Different Types of images by a convex Lens :  Case 1. When the object is at Infinity from a convex lens , then the image formed is :  (i) At the focus,  (ii) Real and Inverted (iii) Much smaller than the object ( or Highly Diminished). Case 2. When the object is beyond 2f , then the image formed is : (i) Between f and 2f on the other side of the lens. (ii) Real and Inverted (iii) smaller than the object ( or diminished ). Case 3. When the object is at 2f , then the image formed is : (i) At a distance 2f on the other side of lens. (ii) Real and inverted  (iii) of the same size as ...

The working of a lens is based on the refraction of light rays when they pass through it . A lens is a piece of transparent glass bound by two Spherical surfaces. There are two type of lenses. Convex lens and concave lens. (i) convex lens : A convex lens is thick at the centre but thinner at the edges and a piece of transparent Spherical glass having a bulge in the middle. Converting lens Convex lens are mainly of three types : (a). Double convex lens : Lenses that has both the surface convex. (b). Plano-convex Lens : Lenses that has one surface plane and the other surface convex. (c). Concave-convex Lens : Lenses that has one surface concave and the other surface convex. (ii) Concave lens : A concave lens is thin in the middle but thicker at the edges and a piece of transparent Spherical glass having a depression in the middle. Diverging lens. (a) Double Concave Lens : It has both the surfaces concave. (b) Plano- concave Lens : It has one surface plane and the other surface concave. (...

Principle of Reversibility - Refraction of light - Param Himalaya  When a ray of light travels from medium 1 (say air) to the medium 2 (say water) along the path AOB, then refractive index of medium 2 w.r.t. medium 1 is given by $${ }^{1}n_{2} = \frac{\sin i}{\sin r} \quad \dots(i)$$ When the path of the ray of light is reversed, it travels from medium 2 (water) to the medium 1 (air) along the path BOA,then the refractive index of medium 1 w.r.t. medium 2 is given by $${ }^{2}n_{1} = \frac{\sin r}{\sin i} \quad \dots(ii)$$ Multiplying eqns. (i) and (ii), we get $${ }^{1}n_{2} \times { }^{2}n_{1} = \frac{\sin i}{\sin r} \times \frac{\sin r}{\sin i} = 1$$ $${ }^{1}n_{2} = \frac{1}{{ }^{2}n_{1}}$$ Or $${ }^{2}n_{1} = \frac{1}{{ }^{1}n_{2}}$$ Thus, refractive index of medium 2 w.r.t. medium 1 is reciprocal of the refractive index of medium 1 w.r.t. medium 2.

Refraction of Light Through a Glass Slab (Lateral shift or displacement) Consider a rectangular glass slab of refractive index $n$ and thickness $t$. Let a ray of light AO be incident at O such that $i$ be the incident angle.After refraction in the glass, the ray of light bends towards the normal NN' and goes along OB such that $r$ is the angle of refraction According to the law of refraction,  $$n_g = \frac{\sin i}{\sin r} \quad \dots (i)$$ At point B, the ray of light again suffers a refraction and emerges out of the glass slab into the air along BC. For refraction at B, $r$ is the angle of incidence and $i$ is the angle of refraction also known as emergent angle. Again, according to the law of refraction,  ${ }^{g}n_{a} = \frac{\sin r_1}{\sin i'} \quad \dots (ii)$ We know that, ${ }^{a}n_{g} = \frac{1}{{ }^{g}n_{a}}$ Using eqns. (i) and (ii), we get, $ \frac{\sin i}{\sin r} = \frac{1}{\frac{\sin r_1}{\sin i'}} = \frac{\sin i'}{\sin r_1}$ $\frac{\sin i}{\sin r} = \fra...

Optically Rarer medium : in which the speed of light is more is known as optically Rarer medium . optically denser medium A medium in which the speed of light is less , is known as optically denser medium. Case 1. Refraction of light when it Goes from rarer medium to a Denser medium : When a ray of light goes from a rarer medium to a denser medium , it bends towards the normal ( at the point of incidence ). In this case , the angle of Refraction (r) is smaller than the angle of incidence (i). Case 2. Refraction of light when it goes from a Denser medium to a Rarer medium. When a ray of light goes from a denser medium to a rarer medium , it bends away from the normal. In this case the angle of refraction (r) is greater than the angle of incidence (i). Case 3 : Refraction of light when light falling Normally ( Or Perpendicularly) on a Glass Slab : If the incident Ray falls normally to the surface of a glass slab , then there is no bending of the ray of light , and it goes straight.

Definition of Refraction of light : The change in direction of light when it passes from one medium to another obliquely is called refraction of light . In other words , the bending of light when it goes from one medium to another obliquely is called Refraction of light. Important terms Related to Refraction: The plane surface that refracts light is known as the surface of refraction. Point of incidence: The point on the surface of refraction , where the ray of light is incident is known as the point of incidence . "O" is the point of incidence. Incident Ray : The ray of light which strikes the surface of refraction at the point of incidence , is known as the incident Ray . AO is the incident Ray. Refracted ray : The ray which travels from the point of incidence to other medium is known as the refracted ray. OB is the refracted ray. Normal : Perpendicular drawn on the surface of refraction at the point of incidence is called normal. NON' is the normal on the surface PQ. A...

Sign convention for Spherical Mirrors ( Concave and convex mirror) : According to new Cartesian sign convention: All distance are measured from the pole of the mirror as origin Distance measured in the same direction as that of incident light are taken as positive. Distance measured against the direction of incident light are taken as negative. Distance measured upward and perpendicular to the principal axis are taken as positive. Distance measured downward and perpendicular to the principal axis are taken as negative. The object is always placed on the left side of mirror. All the distance measured from the pole(p) of mirror to the right side will be considered positive. All the distance measured from the pole (p) of mirror to the left side will be negative. Some important conclusion for sign convention :  The object distance (u) is always negative. If an image is formed behind a concave mirror ( to the right side ) , the image distance (v) is positive. If the image is formed in f...