Light

• Light is a form of energy that enables us to see objects
• Light may be emitted by an object or reflected by it
• Reflection of light is the bouncing back of light in the same medium when it strikes the surface of an object
• Laws of Reflection of Light:

  • The incident ray is the light ray that strikes any surface
  • The reflected ray is the light ray that comes back from the surface after reflection
  • The angle of incidence (∠i) is equal to the angle of reflection (∠r)
  • The incident ray, the normal at the point of incidence, and the reflected ray all lie in the same plane
• Regular Reflection:

  • Occurs on smooth surfaces like a plane mirror
  • If incident rays are parallel, reflected rays are also parallel
  • Produces images and enables us to see everything around us
• Diffused Reflection:

  • Occurs on rough surfaces like a blackboard
  • If incident rays are parallel, reflected rays are not parallel but go in random directions
• Multiple Reflection of Light:

  • Can be obtained by placing more than one mirror at certain angles to each other
  • Used in scenarios like barbershops, kaleidoscopes, and periscopes
  • Periscopes use two plane mirrors to see hidden objects
• Kaleidoscope:

  • Made by joining three rectangular mirror strips to form a prism
  • Creates a variety of patterns when looking through it
  • Designers use kaleidoscopes for new pattern ideas
• Visible light refers to Electromagnetic radiation of wavelength of 300nm to 700nm
• Light does not need any medium to travel
• Speed of light in vacuum is 3 × 10^8 m/s
• Speed of light decreases when it travels in a medium other than vacuum
• Different colours of light have different speeds in media other than vacuum
• Light refracts (bends) when it travels from one medium to another medium (e.g. Air to water or Air to glass)
• Due to different speeds, the bending of different colours of light is different, causing them to separate when entering a medium other than vacuum
• The splitting of light into its constituents is called Dispersion of light
• The sunlight is white in colour and consists of seven colours: VIBGYOR (violet, indigo, blue, green, yellow, orange, and red)
• This arrangement of seven colours of white light is called a Spectrum
• Examples of dispersion of light:Formation of rainbow due to the dispersion of white light through water droplets
• Formation of rainbow due to the dispersion of white light through water droplets
• Passing of Sunlight through a prism
• Dispersion of light through soap bubbles
• Dispersion of light on CDs
• Dispersion Activity:
• Get a plane mirror of a suitable size
• Place it in a bowl filled with water
• Position the bowl near a window so that direct sunlight falls on the mirror
• Adjust the position of the bowl so that reflected light from the mirror falls on a wall
• If the wall is not white, fix a sheet of white paper on it
• Reflected light will be seen to have many colours due to the mirror and water acting as a prism
• Human Eye:
• We see things when light reflected from any object enters our eyes
• The eye has a roughly spherical shape with a tough white outer coat for protection
• The transparent front part of the eye is called the cornea
• Behind the cornea is a dark muscular structure called the iris, which contains a small opening called the pupil
• The iris controls the size of the pupil and the amount of light entering the eye
• Behind the pupil is a convex lens that focuses light on the retina at the back of the eye
• The retina contains cones sensitive to bright light and colour, and rods sensitive to dim light
• Sensations felt by sensory cells are transmitted through nerve cells to the brain via the optic nerve
• Eyes have eyelids for protection and to regulate light entering the eye