Light and Sight

1.Source of light

• Luminous object: object that give out light as the result of the excited atoms receive energy.

• Non luminous object: Object that not send out light.

• Laser: A type of light source in which their excited atoms act together and emit a narrow light.

2.Rays and beams

• Rays travel in straight lines• The path in which light pass= rays• A beam is a stream of light.• Beam of light can be parallel, converging,

diverging.

3.Shadows

• Opaque: Object that doesn’t let light pass• Small source of light give sharp shadows with

dark color all over.• Large large amount of light give a shadows

with a pitch dark on the centre with gray area surrounds it.

• Umbra: Dark region• Penumbra: Gray area

4.Speed of Light

• Very fast• Faster than sound

5.Law of reflection

• Normal : an imaginary line that perpendicular 90 degree to the surface.

• Law of reflection : The angle of incidence equals angle of reflection.

6.Periscope

• Instrument that use 2 mirrors.

7.Regular and diffuse reflection

• Regular reflection is on a smooth surface.• Diffuse reflection is on rough surface.• Diffuse reflection does not follow law of

reflection.

8. Real image and Virtual image

• Real image is the image that can be from on screen and produced by light rays that passed through it.

• Virtual image is the image that cannot be produced on screen and produced by rays that seemed to pass through it but not.

9. Lateral inversion

• This is an effect produced by plane mirror.• Your left and right eyes are interchanged.• Occurs whenever an image is formed by one

reflection.

10. Properties of plane mirror

• As far behind the mirror as the object is in front and the line joining the object and image is perpendicular to the mirror.

• The same size as the object.• Virtual• Laterally inverted

11. Kaleidoscope

• A set of two mirror set at an angle to produce multiple image.

• Formula to find the image produce by two mirrors forming specific angle:

360

X- 1

12. Facts about reflection

• Light ray that enter a denser medium have angle of reflection smaller than angle of incidence.

• A light ray is bent away from the normal when enter a less dense medium.

• A light ray is bent towards the normal if it enters a denser medium.

• A ray emerging from parallel sided block is parallel from ray that enter the block.

• A ray enter at the normal of an object is not refracted.

13. Refraction index

• Refraction happens because change of speed of light.

• Reactive index = Speed of light in air or 1st medium

Speed of light in 2nd medium

14.dispersion

• The spread out of color spectrum when white color light pass through a prism.

15.Critical angle

• The angle at which the angle of refraction is 90 degree.

• When the light does not pass the boundary it is said that it undergo total internal reflection.

16.Multiple images

• It happened because of the multiple reflection inside a glass of mirror which cause blurring.

17.Total reflecting prisms

• The prism which completely reflecting light rays.