Light- Refraction Basics
* The tendency of light to bend at the point of separation of two media is called refraction.
* The ratio of velocity of light in the first medium to that in the second medium is known as the refractive index of the second medium with respect to the first medium.
* The ratio of velocity of light on air or vacuum to that in a medium is called the absolute refractive index (μ) of the medium.
* According to Snell’s law, the ratio between the values of the sine of angel of incidence and the sine of angle of refraction for two given optical media is constant.
μ = \frac{sin \thinspace \thinspace i}{sin\thinspace \thinspace \thinspace r}
* Critical angle is the angle of incidence in a denser medium, for which angle of refraction in the rarer medium is 90°.
* Total internal reflection occurs when the angle of incidence is greater than the critical angle. In such cases, the refracted ray bends by more than 90°, and gets reflected back into the same denser medium.
* The perpendicular distance between incident ray and emergent ray after passing through a glass slab is called lateral shift.
* The change in position of the object and image when seen through a denser medium is called vertical shift.
Refraction by Spherical Lenses
* A lens is a piece of transparent optical material with one or two curved surfaces to refract light rays.
* A convex lens has a surface that bulges outwards on both sides.
* A concave lens has inward bent surfaces on both sides.
* The distance between the optic centre and the focal point is called the focal length.
* Magnification is the ratio of image size to object size. It is also measured as the ratio of image distance to object distance.
m = ( \frac{size \thinspace of \thinspace image}{size\thinspace of \thinspace \thinspace object} ) or m = ( \frac{image \thinspace \thinspace distance}{object \thinspace \thinspace \thinspace distance} )
According to the lens formula:
\frac{1}{f} = \frac{1}{v} – \frac{1}{u}
Where,
f = focal length
u = object distance
v = image distance
Human Eye and Colourful World – Dispersion and Scattering of Light
A prism is a piece of glass or any other transparent material, having two triangular and three rectangular faces. A light ray refract twice as it propagates through a prism.
* Refracting surface are the rectangular faces of triangular prism.
* The refracting edge is the line along which the two refracting surface meet.
* The angle of a prism is the angle between the two refracting faces. It is denoted by capital letter A.
* The base of the prism is one of the rectangular faces of prism that does not take part in refraction.
* The incident ray is the ray of light that is incident on a refracting surface.
* Thee refracted ray is the ray that deviates at the point of incidence and travel inside the prism between two refracting surfaces.
* The emergent ray is the light ray emerging from the prism after refraction.
* Angle of incidence is the angle formed between the refracted ray and the normal at the point of incidence.
* Angle of refraction is the angle between the normal and the refracted ray at the point of incidence.
* Angle of deviation is the angel between the incident ray. It is represented Greek letter δ or θd or D.
* Dispersion is the splitting of light into its constituents, revealing different colours depending on the wavelengths.
* Atmospheric refraction is the apparent random wavering or flickering of object seen due to inconsistency in the physical conditions of the refracting medium such as air.
* Scattering is the deviation of light rays from its straight path.
* Tyndall effect is the scattering of a light beam by colloidal particles, illuminating the path of the beam.
* The Tyndall beam is the illuminated path of a light beam in a colloidal solution.
Refraction- Natural Phenomena
* When a light ray passes through a parallel sided glass slab, it has deviation but it shifts laterally.
The perpendicular distance between an incident ray and an emergent ray is called “lateral shifts” and depends on
* Angle of incidence
* Thickness of the glass slab
* Refractive index of the medium
* Wave length of the incident ray
* The apparent depth of a transparent material like glass or water when viewed from above is less than the actual depth.
Refractive index = \frac{Real \thinspace \thinspace depth}{Apparent \thinspace \thinspace \thinspace depth}
* When an oblique light ray from a heavenly body like the sun enters the atmosphere it continuously moves into regions of high refractive index and hence bends towards the normal. This bending of light through atmospheric air is known as “atmospheric refraction”.