Class 6 Science Chapter 11 Light Shadow Reflection, Propagation of Light, Pinhole Camera (For CBSE, ICSE, IAS, NET, NRA 2022)

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Light Shadow Reflection

Light

  • It is a form of energy which allows us to see objects around us.
  • Some of the light gets reflected the moment light falls on an object.
  • This reflected light when comes to our eyes allows us to see objects.
  • Light travels in a straight line and its speed are faster than sound.
  • Light travels at a speed of m/s.

Experiment

Experiment Cardboard
  • Three cardboards have been taken namely A, B and C.
  • At the same height three holes have been made using a pin.
  • The cardboard pieces have been suspended using separate threads vertically from a support such that each hole is at the same height and in the same line.
  • Near one of the cardboards, the lighter candle is placed and other from the other side of the cardboard, the candle flame is looked at. The candle flame is clearly seen.
  • Now the second cardboard has been slightly displaced such that the holes no longer remain in a straight line.
  • Once again on looking at the candle flame from the other side of the cardboard the candle flame cannot be seen.
  • In first case the candle flame is visible whereas in the second case the candle flame is not visible since light travels in a straight line and the holes in the cardboard A, B and C are not in a straight line.

Properties of Light

Reflection of Light

It is the phenomenon in which light travelling in one medium, incident on the surface of other returns to the first medium.

Refraction of Light

In refraction there is a change in the speed of light as it travels from one medium to another.

Dispersion of Light

It is the phenomenon in which a ray of light splits into its constituent colours.

Diffraction of Light

It is the phenomenon of bending of light around corners in such a way that it spreads out and illuminates՚ areas where a shadow is expected.

Polarization of Light
  • It is the process of transforming unpolarized light into polarized light.
  • An unpolarized light is the light wave propagating in more than one plane.
  • A polarized light is the light wave in which the vibrations occur in a single plane.
Interference of Light
  • It is a special phenomenon reflecting the wave nature of light.
  • There is modification in the intensity of light due to redistribution of light energy.

Luminous and Non-Luminous Objects

  • A luminous object is one that produces light. For e. g. , sun, bulb, etc.
  • A non-luminous object is one that does not produce light. For e. g. , moon, earth, blackboard, etc.

Propagation of Light

  • The way in which an electromagnetic wave transfers its energy from one point to another.
  • When light passes between boundaries from one medium to another three main processes generally occur namely Transmission, Reflection and Refraction.

Propagation of Light through Vacuum

  • There is little or no scattering.
  • Except for objects in the path of the light rays, a beam of light through vacuum will be completely invisible.

Propagation of Light in Solids

  • Scattering of light occurs.
  • The re-emitted photons interfere to support forward propagation.

Transparent, Translucent and Opaque Objects

Transparent, Translucent and Opaque Objects
Transparent ObjectTranslucent ObjectOpaque Object
Allows complete passage to light.Allows partial passage to light.Does not allows passage to light.
Vision is clear.Vision is faint.No Vision.
Examples are glass, water, and air.Examples are frosted glass and wax paper.Examples are Stone, metal, wood.

Image and Shadow

Difference between Image and Shadow
ImageShadow
Formed due to the intersection of reflected rays.An opaque object or material is placed in the path of rays of light.
Light enters the observer՚s eyes.No light enters the observer՚s eyes.
Information such as colour, structure, etc. are given.Shadow doesn՚t provide any such information.
It may be straight or inverted.It is never inverted.

Umbra and Penumbra

Illustrating the Formation of Umbra and Penumbra
Difference between Umbra and Penumbra
UmbraPenumbra
Darkest part of a shadow.Lesser dark part of a shadow.
No light reaches this region.Light from some parts of the source reaches.
Central part of the shadow.Outer part of the shadow.

Pinhole Camera

  • It works on the principle that light travels in a straight line.
  • Consists of two boxes. One of the boxes easily fits into another box and can be slid to and fro.
  • At the front of the camera, there is a pin-sized hole.
  • At the back of the screen there is a translucent screen.
  • Image formed is real, inverted and diminished in size as compared to the original object.
  • To obtain a clear image of the object, the distance between the pin-hole and screen can be adjusted.
  • These cameras are inexpensive and are easy to make.
Image Formed in a Pinhole Camera

Developed by: