Physics - Reflection and Refraction

Introduction

• The natural/artificial agent that kindles sight and makes things visible is known as light.

• Light appears to travel in straight lines.

Reflection of light

• The throwing back by a body or surface of light without absorbing it, is known as reflection of light.

• A highly polished surface, such as a mirror or other smooth and plane surface, reflects most of the light falling on it.

• Reflection of light is either specular (just like mirror) or diffuse (retaining the energy.

Laws of Reflection of Light

• Following are the significant laws of reflection −

  • The angle of incidence is equal to the angle of reflection, and

  • The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.

• The laws of reflection described above are applicable to all sorts of reflecting surfaces including spherical surfaces.

• Image formed by a plane mirror is always virtual and erect.

Spherical Mirror

• The spherical mirror, whose reflecting surface is curved inwards (as shown in the image given below), i.e. face towards the center of the sphere, is known as concave mirror.

• The spherical mirror, whose reflecting surface is curved outwards (as shown in the image given below), is known as a convex mirror.

• The center of the reflecting surface of a spherical mirror is a point known as pole represented by English letter ‘P.’

• The reflecting surface of a spherical mirror forms a part of a sphere, which has a center, known as the center of curvature represented by English letter ‘C.’

• Remember, the center of curvature is not a part of the mirror, but rather it lies outside the reflecting surface.

• In case of concave mirror, the center of curvature lies in front of it.

• In case of convex mirror, the center of curvature lies behind the mirror.

• The radius of the sphere of which, the reflecting surface of a spherical mirror forms a part, is known as the radius of curvature of the mirror and represented by the English letter ‘R.’

• Remember, the distance pole (P) and center of curvature (C) is equal to the radius of curvature.

• The imaginary straight line, passing through the pole and the center of curvature of a spherical mirror, is known as the principal axis (see the image given below).

• All the reflecting rays meeting/intersecting at a point on the principal axis of the mirror; this point is known as principal focus of the concave mirror. It is represented by English letter ‘F’ (see the image given below).

• On the other hand, in case of convex mirror, the reflected rays appear to come from a point on the principal axis, known as the principal focus (F) (see the image given below).

• The distance between the pole (P) and the principal focus (F) of a spherical mirror is known as the focal length and it is represented by the English letter ‘f’ (see the image given above).

• The diameter of the reflecting surface of spherical mirror is known as its aperture.