Students' Contributions



Topics for discussion:

1.Properties of light
  • Reflection
  • Refraction
  • Speed of light

2. Defects of vision
  • Accomodation
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  • Short-sightedness (Myopia)
  • Long-sightedness (Hyperopia)
  • Astigmatism
  • Colour-blindness
    • Colour blindness
      Colour blindness
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  • Presbyopia

3. Limitations of sight
  • Optical illusions
  • The blind spot

4. Stereoscopic and monocular vision
  • Stereoscopic vision
  • Monocular vision

5. Devices used to overcome the limitations of sight
  • Telescope
  • Binoculars
  • Microscope
  • Periscope
  • Ultrasound scanning device (Ultrasonography)




1.7 Light and Sight



Characteristics of light


1. Light travels in a straight line.

a. This characteristics of light leads to occurrences such as shadow formation, eclipse of the Sun and eclipse of the Moon.

b. An object which allows light to pass through it, is called a transparent object. Examples : A prism and a clear glass.

c. An object which does not allow light to pass through it, is called an opaque object. Example : Wood and paper.

d. Shadows are formed when light is blocked by opaque objects.

e. The formation of a shadow depends on the size and angle of the source of the light.

  • Umbra is the dark shadowy area.
  • Penumbra is the shadowy area that is not clear.

f. Two natural phenomena that occur due to the characteristic of light travelling in a straight line are :
  • A lunar eclipse that occurs when the Earth is situated between the Moon and the Sun. The shadow of the Earth falls on the surface of the Moon to appear invisible.
  • A solar eclipse that occurs when the Moon is situated between the Earth and the Sun. The shadow of the Moon falls on the surface of the Earth and causes that part of the Earth to experience darkness.

Alia Syakiera.




Reflection and Refraction of Light

Light changes in direction by reflection and refraction. These properties occur during our daily life.

E.g : Refraction of Light : A stick to appear bent in water and a swimming pool to appear shallower.

Reflection of light : Diamonds sparkle because they reflect light falling on them.

~kah long~ =)





Reflection of Light


1. Light which falls on an object is reflected by the object onto our eyes. The reflected light allows us to see the object.

2. An opaque object does not allow light to pass through it. Some of the light will be
absorbed and some of it will be reflected.

3. Reflection of light depends on:

  • The colour of the object
    • A bright object reflects more light than a dark object.
  • The condition of the object's surface
    • Flat and smooth surfaces reflect more light than rough and uneven surfaces.

4. The characteristics of the image on a plane mirror.
  • Unreal (cannot) be traced on the screen
  • Vertical
  • Reverse-sided
  • Same size as the object
  • The distance of the object from the plane mirror is the same as the distance of the image from the plane mirror.

Aisyah Zainal



external image lavalampnightlight.jpg

Properties of Light
1. Light travels in a straight line
2. Light can be refracted
  • bending of light ray when it enters a medium of different density
- e.g. Medium to higher density : the speed increases
Lower to higher density : the speed decreases
3. Light can be reflected
4. Light acts as an electromagnetic wave
  • external image Young_Diffraction.png
- Thomas Young's Wave Theory
5. Light travels 300 000 000 000 000 m/s in vacuum
  • external image Speed_of_light_from_Earth_to_Moon.gif
- Diagram : speed of light from the Earth to the Moon

Extra Information
How A Prism Works
external image rainbow-prism.jpg

Done by,
Aishah Nadirah
LIGHT
- When light is travels from a medium of lower density to a medium of higher density the speed of light decreases.
REFLECTION
- Reflection of light occurs when light
bounces off the surface of an object.
REFRACTION
- Light can travel through difference medium such as air, water, glass and plastic.
- Speed changes when light travels from one medium to another.
- The bending of light ray when it enters a medium of different density is known as refraction of light.

Light and Sight
1. Light travel
- In a straight line
- 3x10 power of 8 ms-1
- Through vacuum (sound cannot travel through vacuum

2. Light can travel
- Through transparent media (air, water, glass, plastic and etc.)
- From one medium to another but the speed changes

Reflection and Refraction
- Reflection of light occurs when light bounces off the surface of an object.
- The bending of a light ray when it enters a medium of different density is known as the refraction of light.
- When light travels from a medium of lower density to a medium of a higher density, the speed of light decreases.
- When light travels from a medium of higher density to a medium of a lower density, the speed of light increases.

Law of Reflection
Law of reflection states that when a ray of light reflects of a surface, the angle of incidence is equal to the angle of reflection and the incident ray is on the same place.

Short-sightedness (Myopia) and Long-sightedness (Hyperopia/Hypermetropia)
1. Short- sightedness
- Can see near objects
- Cannot focus on distance object
Causes
- Distance object is focus in front of the retina
- Eyeball is too long
Corrected
- Use a concave lens

2. Long-sightedness
- Can see far objects
- Cannot focus on near objects
Causes
- Near objects is focus at the back of the retina
- Eyeball is too short
Corrected
- Use a convex lens

Astigmatism**
Caused
- Irregular surface of the cornea
- See some parts of an object more clearly than other parts
- See lines in one direction clearer than other lines in other direction
- May see world as a distorted images

Corrected
- Use a cylindrical lens
- Go through surgery

Done by,
Melanie Foong