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Contents : Light Laws of Reflection Regular & Diffused Reflection Luminous & Non – Luminous Objects Real & Virtual Images Power of Accommodation
Least Distance of Distinct Vision Short – Sightedness Long – Sightedness Persistence of Vision Perception of Colour Fascinating Facts Some Interesting Pictures
Light Light is a form of energy. Light travels in a straight line. Light enables us to see the objects around us. The light reflected from objects falls into our eyes & thus, we can see the objects. Dispersion of light is splitting of white or some other light into its components.
Laws of Reflection The light ray which strikes any surface is called the Incident Ray. The ray that comes back from the surface after reflection is known as the Reflected Ray. The perpendicular to the surface at the point of incidence is known as Normal.
• The angle between the normal and incident ray is called the Angle of Incidence.• The angle between the normal and the reflected ray is known as the Angle of Reflection.• The angle of incidence is always equal to the angle of reflection.• This is known as the Law of Reflection.
Regular & Diffused ReflectionReflection from a smooth surfacelike that of a mirror is calledRegular Reflection.When all the parallel rays reflectedfrom a plane surface are notparallel, the reflection is known asDiffused or Irregular reflection.
Luminous & Non – Luminous Objects• Those objects which emit their own light are called Luminous Objects.• The objects which do not emit light of their own, but they reflect light falling on them, are called Non – Luminous Objects.
Real & Virtual Images The image formed when incident rays after reflection actually meet at a point is known as a Real Image. The image formed when incident ray after reflection do not actually meet, but appear to meet at a point is knows as a Virtual Image.
Power of Accommodation The ability of the eye to focus the distant objects as well as the nearby objects at the retina by changing the focal length or converging power of its lens is known as the Power of Accommodation.
Least Distance of Distinct Vision The minimum distance at which an object must be placed so that a normal eye may see the object clearly without any strain on the eye is known as the Least Distance of Distinct Vision. It is about 25cm for a normal eye.
Short – Sightedness Myopia or Short Sightedness means a person can see only nearby objects clearly, but cannot see distant objects. This defect is removed by using a concave lens.
Long – Sightedness Hypermetropia or Long – Sightedness is the reverse of Myopia. A person suffering from this defect can see distant objects clearly, but not nearby objects. The defect is removed by using convex lens.
Persistence of Vision Impression of an image on the retina lasts for 0.1 sec after the removal of the object. This effect is known as Persistence of Vision.
Perception of Colour The human eye contains a large number of cell rods and cones which are sensitive to light. The rods respond to the intensity of light and the cones respond to the colour of the light. If cone cells are absent in the eye, then such a person is Colour Blind.
Fascinating Facts A ray of light is an idealisation. In reality, we have a narrow beam of light which is made up of several rays. For simplicity, we use the term ray for a narrow beam of light.