hello, readers today we discuss about the main laws of ray and definition of reflection, refraction and Total Internal Reflection. hope you will understand.

 Reflection, Refraction and Total Internal Reflection

1.1 Reflection

We see most of the things with the help of light reflected from them. When a ray of light falls on the boundary separating two optical media, light is partly reflected into the first medium and partly transmitted into the second. If the surface is smooth (polished mirrors, metals, liquid surfaces etc), it reflects light specularly and is known as specular reflection. However, many surfaces have microscopic irregularities, then it reflects light at many angles and the reflection is diffuse. In physics, the term reflection is used to mean specular reflection.

Laws of reflection :
  • Mirror reflection
  • Specular reflection
  • Diffuse reflection


The incident ray, reflected ray and the normal to the surface all lie in the same plane.

The angle of reflection θ2 is equal to the angle of incidence θ1.

1.2 Refraction

The light ray that enters a transparent medium from another transparent medium is bent at the boundary and is said to be refracted. The boundary is known as a refracting surface. The angle of refraction ‘T’ depends on the properties of the two media and on the angle of incidence ‘i’ –

Sin(i) / sin(r) =  V1/ V2

where V1 is the velocity of light in medium 1 having refractive index PI and similarly where V2 is the velocity of light in medium 2 having refractive index ’12. The relation is more popularly known as Snell’s law. It follows from Snell’s law that an increase in the angle of incidence causes an increase in the angle of refraction. When a light ray passes from rarer to a denser medium, it is bent towards the normal in the denser medium and vice-versa. Further, for a given angle of incidence, the angle of refraction depends on the wavelength of the incident ray and varies from color to color.

1.3 Total Internal Reflection

A medium having a lower refractive index is said to be an optically rarer medium while a medium having a higher refractive index is known as an optically denser medium. When a ray of light passes from a denser medium to a rarer medium, it is bent away from the normal in the rarer medium. Snell’s law for this case may be written as,

Sinr = P1sin(i) /P2

where ‘i’ is the angle of incidence of a light ray in the denser medium and ‘r’ is the angle of refraction in the rarer medium.

At some particular angle of incidence ‘i’, the refracted ray glides along the boundary surface so that r = 90°. The angle ‘ic’ is known as the critical angle. At angles greater than ‘ic’, there are no refracted rays at all. The rays are reflected back into the denser medium as though they encountered a specular reflecting surface. The phenomenon in which light is totally reflected from a denser-to-rarer medium boundary is known as total internal reflection.

hope you readers know better by reading this blog. if you have any query related to this comment below. You can also read our previous blog about detection and application of ultrasound Thank you

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