Back to Lesson

• Properties of light
  • Light travels in a straight line
  • Light travels at very fast speed.
  • Light does not require any medium to travel.
  • When light strikes a surface, it bounces back, it is called reflection of light.
  • Light can pass through some material by bending through it. This is called refraction of light
  • Light is composed of many colors
• Reflection – Bouncing back of the light after striking a surface is called reflection
• Terms used in reflection
  • Beam of Light: A highly focused light that goes in one direction is a beam of light.
  • Ray of light: A very fine beam of light is treated as ray of light.
  • Parallel Beam or Collimated Light: When light rays are travelling parallel to each other the light is called parallel beam or collimated beam.
  • Incident Ray and Reflected Ray: The ray which strikes any surface is called the incident ray and the ray that come from the surface after reflection is called the reflected ray.
  • Normal: If you draw lines showing the mirror, the incident ray and the reflected ray and make a line perpendicular to the surface of mirror at point of intersection of incident and reflected ray then the line is called the normal.
  • Angle of Incidence (ㄥi) : The angle made by incident ray with the normal is called angle of incidence.
  • Angle of Reflection (ㄥr): The angle made by reflected ray with the normal is called the angle of reflection.
• Laws of reflection –
  • The angle of incidence is always equal to the angle of reflection.
  • The incident ray, the reflected ray, and the normal at the point of incidence, all lie on a plane.
• Plane mirror: Mirror in which you look have a smooth, flat front surface and a coating of shiny material on backside of the mirror. e.g. steel plate, computer screen, smooth floor, lake with clear water.
• Spherical mirror: mirror with curved surface. These are concave and convex mirror.
• Concave mirror: mirror is curved inwards. E.g inward curved surface of a shiny spoon, the curved reflectors in torches, and in headlights of vehicles,
• Convex mirror: mirror is curved outwards. E.g. curved surface of a shiny spoon, vehicle mirrors, steel balls, Supermarket mirrors etc
• Difference between concave and convex mirrors
  

  Concave mirror	Convex mirror
  Inner side of spherical mirror is reflecting	Outer side of spherical mirror is reflecting
  Image is formed depending on the position of the object	Image formed is real inverted and diminished
  E.g inward curved surface of a shiny spoon, the curved reflectors in torches, and in headlights of vehicle	E.g. curved surface of a shiny spoon, vehicle mirrors, steel balls, Supermarket mirrors etc

• Virtual image – Image that can be seen but not obtained on the screen
• Real image – Image can be obtained on screen
• Lens – material which is transparent and have one or both curved surfaces
• Convex lens / converging lens – lens which is thicker at the center as compared to edges
• Concave lens / diverging lens – lens which is thinner at the center as compared to edges
• Image formation by concave and convex lens
  

  Position of the object	Position of the image	Relative size of the image	Nature of the image
  At infinity	At focus F2	Highly diminished and point size	Real and inverted
  Beyond 2F1	Between F2 and 2F2	Diminished	Real and inverted
  At 2F1	At 2F2	Same size	Real and inverted
  Between F1 and 2F1	Beyond 2F2	Enlarged	Real and inverted
  At focus F1	At infinity	Infinity large or highly enlarged	Real and inverted
  Between focus F1 and optical centre O	On the same side of the lens as the object	Enlarged	Virtual and erect

• Color in white light – Violet, Indigo, Blue, Green, Yellow, Orange, Red
• Recombination of light – If the color of white light from the prism is allowed to fall on the inverted prism again the white light appears
• Primary colors of light – red, blue, and green colors
• Secondary color of light – colors which are formed by combination of red blue and green light
• Complementary colors of light – when white light can be produced by combining two colors
• Mutually complementary colors of light – If one of the color in such pair is primary and other is secondary