Improve Your Learning - Reflection of Light

 Important Points in Reflection of Light at Curved Surfaces:

• Light always travels straight in line.  This is called Rectilinear motion of Light.
• To form a shadow we need a Source of Light, Object (Opaque substance) and a Screen. 
• "When Light gets reflected from any surface, it selects a path which takes the Least time".  This means light travels in a straight line.  This is called Fermat's Principle.
• Two laws of reflection are there and they are 1) Always the angle of incidence is equal to angle of reflection.  2) The incident light ray, the normal line at the point on a surface of incidence and reflected light ray all lie in same plane.
• The size of the image formed by the plane mirror is equal to the object. 
• The characteristics of the image formed by the plane mirrors are Virtual, erect or upright, inside the mirror and same distance as the object from the mirror.
• We can observe lateral inversion in the images formed by the plane mirrors.  Lateral inversion means if we lift the right hand up, in the image appears as left, similarly if u lift the left hand appears as right hand in the image.
• The images which can be only seen inside the mirror and which can not be caught on the screen are called Virtual images.
• The images which can be caught on the screen are called Real images.
• The rays which diverge after reflection form Virtual Images.  Similarly the light ray which converged after reflection form Real images.
• The two laws of reflection are applicable for all types of mirrors and surfaces including curved surfaces. 
• The reflecting surfaces which have curved surfaces are called spherical mirrors and Convex and Concave mirrors are best examples for spherical surfaces.  Inner and outer surfaces Spoon and bowl also few examples for the spherical surfaces.
• Spherical mirrors are usually a part of any sphere. 
• Generally spherical mirrors can have two surfaces, inner and outer.  If the inner surface acts like a mirror then it is called a Concave mirror, whereas if the outer surface or bulged surface acts like a mirror then it is called a Convex mirror.
• Most of the images formed by the concave mirror are real images, very few are virtual images. 
• Convex mirror always forms a virtual image. 
• The Geometric Centre (Mid Point) of the mirror is called a Pole and is denoted with 'P.'
• The Centre point of the sphere from which the curved surface is prepared is called the "Centre of Curvature" and lies at the same distance from the curved surface as when it is combined with the sphere. The Centre of Curvature is denoted with 'C.'
• The distance between Pole and Centre of Curvature is called Radius of Curvature or The distance between any point on the curved surface to the Centre of Curvature is called Radius of Curvature.  Radius of Curvature is denoted with 'R'.
• The passes by combining Pole and Centre of Curvature are called Principal Axis.
• The light rays which travel parallel to the Principal axis, incident on the concave mirror and after reflection all the ray intersects the principal axis at a particular point.  This point is called Focus in case of a concave mirror. 
• The light rays which travel parallel to the Principal axis, incident on the convex mirror and after reflection all the rays appear to be emerging from a particular point on the principal axis.  This point is called Focus in the case of convex mirrors. 
• Focus or Focal Point is denoted with 'F'.
• The distance between Pole and Focus is called Focal Length.  Focal Length is denoted with 'f'.
• Radius of Curvature is double to Focal Length R=2f.
• The distance between Pole and the place of the object is called as Distance of Object and it is denoted with 'u'.
• The distance between image and the place of image is called Distance of Image and it is denoted with 'v'.
• To measure all the distances we need to follow sign conventions parameters.
• The sign convention parameters are 1) All the distances must be measured pole, which means while measuring distances we need to start from Pole. 2) The distances measured in the direction of the incident light ray are taken as positive, and the distances measured in the direction opposite to the incident light ray are taken as negative. 3) Height of the object or image if above the principal axis are taken as positive, if below the principal axis are taken as negative.
• Any two rays emerging from a point of an object are used to locate the image.
• The ray parallel to the principal axis, after reflection passes from the focal point for the concave mirror.
• If the incident light ray passes through the focal point after reflection it becomes parallel to the principal axis in case of concave mirror.
• The incident ray parallel to the principal axis after reflection from the convex mirror it appears to be emerging from the focal point.
• If the incident light ray which seems to move towards the focal point of a convex mirror, after reflection it becomes parallel to the principal axis.
• The ray which passes from the Centre of Curvature(Along Normal Line) after reflection retraces the same path or bounces back in the same path.
• When an object is placed between Pole and Focal point in the case of a Concave mirror, the image is formed inside the mirror, enlarged(bigger in size), erect and virtual image is formed. 
• When the object is placed on Focus in front of a Concave mirror, the image is formed at an infinite distance.
• If the object is placed between Focus and the Centre of Curvature in front of a Concave mirror, the images are formed outside the Centre of Curvature.  The Characteristics of the image is Real, Outside C, enlarged and inverted.
• If the object is placed on the Centre of Curvature before a Concave mirror, the image also forms in the same place.  The characteristics of the image are Real, On C, Same in Size and inverted.
• If the object is placed beyond the Centre of Curvature before a Concave mirror, the image is formed in between Focus and Center of Curvature.  The characteristics of the image are Real, Between F and C, Smaller in Size and inverted.
• Convex mirror always forms an image between Focus and Pole, Small in Size, Erect and Virtual image irrespective of the position of the object.
• During the formation of images by spherical mirrors the images may diminish or enlarge this is called Magnification. Magnification M= -v/u or hi/ho.  v= distance of the image, u=distance of the image, ho=height of the object, hi= height of the image.
• The relation among focal length, distance of object and distance of image is called Mirror Formula.  The Mirror Formula is  1/f=1/v+1/u.  Focal Length is always positive for Convex Mirrors and negative for Concave Mirrors.
• Solar cookers and TV dishes are the best examples for Concave surfaces.
• Rare view mirrors in the Vehicles are the best example for Convex Mirrors.