Light energy:
- is emitted from luminous objects
- reflects off some surfaces and object
- is absorbed by certain surfaces
- is refracted by transparent objects
- is transferred by radiation
What are luminous objects
- is a light source that radiates light energy
- eg.the sun,stars,candles
What are non luminous objects
- are not a source of light energy itself, but it reflects the light of a luminous source
eg. moon and planets
What is a propagation
-light moves in a straight line
What are the properties of image formed by the pinhole camera
- the image is inverted (upside down)
- the image is real
What is radiation
-Light is radiated in a similar way to heat being radiated from a barbecue fire
How does light travel
-travels through empty spaces,which is why it is possible for rays of the sun to reach the earth
What is the spectrum of visible light
-it refracts white light into the colours of the spectrum
What are the colours of the dispersion
- red
- orange
- yellow
- green
- blue
- indigo
- violet
How does a dispersion work
- the prism refracts white light twice
- at the first separation level it is refracted towards the normal
- at the second separation level it is refracted away from the normal
- after the second refraction of white light the complete spectrum is visible
What is normal
- the perpendicular line (90’) to the surface where the light ray hits the surface.
- It is necessary to use the normal because not all surfaces are flat
- It is difficult then to measure angles accurately
What differs from the prism every colour emerging
- the angle
The angle of a prism differs, this means
-that every colour moves through the prism at a different velocity
What happens with violet
- has the most energy
- highest frequency
- shortest wave length
- light is refracted the most
What happens with Indigo
- slightly less energy
- slightly lower frequency
- longer wave length
What happens with red
- with the least energy
- lowest frequency
- longest wave length
- red light is refractured the least
What is transparent substances
- allow most of the light through and you cans through it
- reflects some of the light
- absorb some of the light
eg. clear glass,plastic, clean water
What is translucent
-allow light through, but you can not see through it
eg matt glass
What is opuque
-do not allow light through and you cannot see through it
eg metal and wol
-they:
-absorb or reflect light
-cause shadows on the sides away from the light source
What is absorption
-light energy is absorbed differently by different objects
What happens with transparent coloured objects
-when red light and green light, respectively, fall on a red filter, only the red light is let through
The red filter absorbs all other colours and allows only red light through, same with green
What happens with opaque objects
-absorb all other colours and only reflects the colour of the object
-only this reflected colour reaches your eyes that is the colour of the object
eg. white light on red paper=red light
red light on red paper=red light
What is reflection
- objects that are not luminous, can only be seen when light is reflected off it
- therefore light rays must sine on the object
- most surfaces reflect light
eg. light rays from the sun
What is a smooth surface
- with reflection, the angles of incidence and reflection are equal
- the angle of incidence is between the incident rays and the normal
- the angle of reflection is between the reflection ray and the normal
eg. a mirror reflect same direction
