Visible light waves:
Electromagnetic waves, their wave length ranges between “380 : 700” nanometre.
Light velocity:
The distance travelled by light in one second = 3 108 m/sec.
The main source of light is the sun.
Light analysis:
- The white light consists of (7) colours called spectrum colours (Red – Orange – Yellow – Green – Blue – Indigo - Violet)
- Light can be analyzed by (Triangular prism)
- Energy of light quantum is composed of (Photons)
- Energy of light quantum = constant (Planck’s constant) Frequency of photon
Light behaviour in different media: Media can be classified due to their ability to allow light to pass through into:
1- Transparent:
That primits light to pass (air – pure water).
2- Opaque:
Doesn’t primit light to pass (paper – wood)
3- Semitransparent (translucent):
Primits part of light to pass and absorb another part.
Ex: rough glass.
- The increase in thickness of transparent medium decreased its ability to transmit light through.
- Light travels in straight lines can be controlled in its thicknes.
Light intensity (Brightness):
- The amount of light that falls perpendicular to a unit area unit area in one second.
- Light intensity decreases by increasing the distance between the surface and source of light.
The Inverse Square Law:
The light intensity that falls of a surface is inversely proportional to the square of distance between the surface and the source of light.
Reflection and refraction of light
Light reflection:
The rebounding of light waves when they fall on reflecting surface.
Kinds of reflection:
1) Regular reflection:
The reflected rays rebound in one direction when they fall on smooth surface.
2) Irregular reflection:
The reflected rays rebound in many directions when they incident on a rough surface.
Laws of Light Reflection:
1) Angle of incidence = angle of reflection
2) The incident light ray, reflected light ray and the perpendicular line are all in one point perpendicular to the reflecting surface.
Note:
If an incident light ray is perpendicular on a reflecting surface, it reflects on itself because angle of incidence = angle of reflection = zero
Some instruments that depend on light reflection:
1) Periscope:
Used in submarines and watching dangerous reactions.
2) Optical fibers:
Used in medical scopes
Light refraction:
The change in direction of light due to its transference from transparent medium to another with different optical density.
Optical density:
The ability of transparent medium to refract the light rays.
Angle of incidence:
The angle between incident light ray and the perpendicular line.
Angle of refraction:
The angle between the refracted ray and the perpendicular line.
Emergency angle:
The angle between emergent light ray and perpendicular line.
Laws of light refraction:
1) When light transfers from low optical density to high optical density, it refracts near the perpendicular line.
2) When light transfers from high optical density to low optical density, it refracts far from the perpendicular line.
Refractive index is more than 1
Critical angle:
If the refraction angle in the medium of low optical density equal 90o, the angl in the medium of the high optical destiny is the critical angle of this medium.
Total internal reflection:
When light ray falls from high optical density with incident angle is greater than the critical angle, it reflects to the same medium.
Natural phenomena:
Related to reflection and refraction:
1) Seeing objects with up normal shape.
2) Seeing objects in virtual positions.
3) Mirage.
Reproduction in flowering plants
Flower:
Short stem whose leaves are modified to do reproduction function.
Structure of typical flower:
* The flower grows on floral bud.
* The flower consists of four floweral whorls exist on a swallen part called receptacle.
1) Calyx: green leaves to protect inner parts of flower called sepals.
2) Corolla: colored leaves to attract insects called petals.
3) Stamen: threads called filament ending with anther(group of stamens are called Androcium).
4) Pistil: consists of (stigma – style and ovary) (group of pistils are called genocium)
Types of flowers:
Monosexual:
a- Male contain (calyx – corolla – and stamen)
b- Female contain (calyx – corolla and pistil)
2) Bisexual contain male and female organs (calyx – corolla – stamen – pistil)
Reproduction in plants:
1) Asexual reproduction by (vegetation using green parts)
2) Sexual reproduction
Pollination:
Is the transfer of pollen grains from anther to stigma.
Kinds of pollination:
1) Self-pollination:
In the same flower.
2) Mixed pollination:
Between two flowers.
Pollination can be done by different methods:
1) Air (wind)
2) Insects
3) Man (Artificial pollination)
Fertilization:
Fusion of nucleus of male cell with nucleus of female cell to from (zygote).
A sexual reproduction (Vegetation)
Done by parts of roots or stem or leaves or buds.
Types of asexual reproduction: