# Ch – 10 Light (Reflection)

Important Notes:

• If an opaque object on the path of light becomes very small, light has a tendency to bend around it and not walk in a straight line. Then this effect is known as “Diffraction of light“.
• Laws of reflection of light are –
• The angle of incidence is equal to the angle of reflection.
• The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.
• Properties of image formed by a Plane mirror –
• Image is erect & virtual
• Size of image = Size of object
• Image formed is as far behind the mirror as the object is in front of it
• Image is laterally inverted
• Most common type of curved mirror is spherical mirror.
• The mirrors whose reflecting surfaces are spherical are called “Spherical Mirror“.
• A spherical mirror whose reflecting surface is curved inwards is called “Concave Mirror“.
• A spherical mirror whose reflecting surface is curved outwards is called “Convex Mirror“.
• The centre of the reflecting surface of a spherical mirror is called “Pole“. It is represented by the letter P.
• The reflecting surface of a spherical mirror forms a part of a sphere. This sphere has a centre, which is known as “Centre of Curvature of Spherical Mirror“. It is represented by letter C.
• The centre of curvature in concave mirror lies in front of it while in convex mirror it lies behind the mirror.
• The radius of the sphere of which the reflecting surface of a spherical mirror forms a part, is called the “Radius of Curvature of Mirror“. It is represented by the letter R.
• A straight line passing through the pole and the centre of curvature of a spherical mirror is known as “Principal Axis“.
• The diameter of the reflecting surface of a spherical mirror is called its “Aperture“.
• The distance between the pole and the principal focus of a spherical mirror is called the “Focal Length“. It is represented by the letter f.
• For small spherical mirrors of small apertures, the radius of curvature is found to be equal to twice the focal length i.e. R = 2f.
• The point where a beam of light parallel to the principal axis appears to diverge or converge from a point on principal axis is known as “Principal Focus“. It is represented by the letter F.
• The image formed by a concave mirror depends on the position of the object in relation to points P, F and C.
• Concave mirrors are commonly used in torches, search-lights and vehicle-headlights.
• Convex mirrors are commonly used as rear view mirrors in vehicles.
• The distance of the object from its pole is called the “Object Distance (u)“.
• The distance of the image from the pole of the mirror is called the “Image Distance (v)“.
• The distance of the principal focus from the pole is called the “Focal Length (f)“.
• Mirror formula is 1/v + 1/u = 1/f.
• Magnification is expressed as the ratio of the height of the image to the height of the object.