Contents
The study of Physics Topics can help us understand and solve real-world problems, from climate change to medical imaging technology.
What is Spherical Refracting Surface? What are the Terms Related to Refraction?
Introduction
We have discussed in the previous chapter the refraction of light at a plane surface separating two transparent media and the formation of image due to it. If the surface of separation be spherical (concave and convex), how light will be refracted and how image will be formed will be discussed in the present chapter. The refraction of light in lens and its principle of action can easily be understood from refraction of light at spherical surface.
Spherical Refracting Surfaces
A spherical refracting surface is the part of a sphere separating two transparent media.
The spherical refracting surfaces are of two types :
- Concave spherical refracting surface which is concave towards the rarer medium [Fig(a)].
- Convex spherical refracting surface which is convex towards the rarer medium [Fig(b)].
A Few Terms Related To Spherical Refracting Surfaces
Pole: The mid point P of the spherical refracting surface is called the pole of the surface [Fig.].
Centre Of curvature : The centre of the sphere C, of which the curved refracting surface forms a part is called the centre of curvature of the surface [Fig.].
Radius Of Curvature : The radius of the sphere of which the refracting surface is a part is called the radius of curvature of the surface. In Fig., PC is the radius of curvature (R) of each surface. It is equal to the distance of the centre of curvature from the pole of the surface.
Principal axis : The straight line joining the pole and the centre of curvature of the spherical refracting surface is called the principal axis of the surface. In Fig., the line PC extended both ways is the principal axis.
Aperture : The effective diameter of the refracting spherical surface exposed to the incident light is called the aperture of the surface. In Fig., the line joining M and M’ i.e., the line MM’ is the aperture of the spherical refracting surface.
Sign Convention
i) All distances are measured from the pole of the spherical surface.
ii) The distances measured from the pole in the direction opposite to the direction of the incident ray are taken as negative and those measured in the direction of the incident ray are taken as positive.
iii) If the principal axis of the spherical refracting surface be taken as x -axis, distances along y -axis above the principal axis are taken as positive and distances along y -axis below the principal axis are taken as negative.
Assumptions :
While studying refraction through spherical surfaces following assumptions are made :
- The aperture of the spherical refracting surface is small,
- Refraction of only paraxial rays will be considered.
- The object will be a point object and will lie on the principal axis.