P4 SCIENCE NOTES - LIGHT

							Name : ____________________________                                  Worksheet : Light 1
Class : ________                                                     Date : ________


                           P4 GEP SCIENCE NOTES - LIGHT

Learning Outcomes
1. To recognise that energy is required to make things work or move.
2. To state that living things need energy to carry out life processes.
3. To recognise that the Sun is our primary source of light and heat energy.
4. To infer that an object can be seen when it reflects light or when it is a source of
   light.
5. To investigate the transparency of materials to light.
6. To recognise that a shadow is formed when light is completely or partially blocked
   by an object.
7. To differentiate the ways in which plants and animals obtain their food.



Importance of Light
Energy is required to make things work or move. Light is an important form of energy.
Light energy can be transferred in various ways.

The most important transfer of light energy occurs during photosynthesis. In
photosynthesis, plants use light energy from the sun, water and carbon dioxide to
produce sugars as stored chemical energy. Animals cannot make their own food. When animals
eat plants, the stored chemical energy stored in the food is passed to them.

Some materials that can generate electric current when light falls on them. Eg. solar
cells and calculators.

Light is needed for us to see things.

Light Sources
Light comes from a variety of sources. Objects that emit or give off their own light
are said to be luminous.

Luminous light sources can be either natural or artificial. Our most important source of
natural light is the sun. This tremendous mass of incandescent gas, produced by nuclear
fusion, provides the earth with light and other types of energy. Fireflies, glow-worm
and deep-sea fish produce light through chemical reactions.

Non-luminous objects do not produce light, but are seen because they reflect light
from another light source. The moon and planets receive light from the sun and reflect
it; They are non-luminous or illuminated objects.

Artificial light is made by people. Common sources of this kind of light are candles,
fluorescent lights, and neon lights. Electricity is commonly used to produce artificial
 light. However, electricity is generated by water power or steam power from coal. Both
 power sources can be traced back to the sun.



 How light travels?
 Light travels very fast, about 300,000km/s. It travels faster than sound.

 Light can travel through vacuum. This enables sunlight to reach the Earth.

 Light travels in a straight line.

 When light falls onto an object, three things could happen: reflected, transmitted or
 absorbed.

 Shadow
 A shadow is formed when light is (completely or partially) blocked by an object.
 (Partially blocked light rays --> partial shadow)

 The formation of shadows and the straight edges of shadows provide evidence that
 light travels in straight lines.

 The position, shape and size of a shadow can change. It depends on the positions of the
 light source and the object. A longer shadow is formed when the sun is low in the sky,
 such as in the evening. A shorter shadow is formed at noon.

 An area in shadow appears darker than the area around it because less light is reaching
 it, so less light is reflected into our eyes.

 Reflection
 An object can be seen when it reflects light or when it is a source of light.

 Light rays are reflected when they bounce off an object. Light rays that are not
 reflected off an object (that do not allow light to pass through) are absorbed.

 Light interacts with objects in different ways
 Different materials allow different amount of light to pass through: transparent,
 translucent and opaque.

 Shiny surfaces reflect light better than dull surfaces.

 A beam of white light passing through a prism forms a spectrum of colours. (ROYGBIV)

 Recommended Reading List
* 1."Sciencing" textbook Chapter 4 and 6
 2.
 2. Light travels in straight lines : "www.le.ac.uk/se/centres/sci/selfstudy/lac1.htm"
 3. Science Made Simple "www.sciencemadesimple.com/sky_blue.html"
Some interesting facts...


Technology :The smart clothes that could be used as camouflage.
Sarah Taylor, at the Scottish College of Textiles, is experimenting with
weaving fibre-optic strands with translucent nylon to create fabrics
which can transmit information and emit light. She has been approached
by Britain's Ministry of Defence for whom intelligent clothing would be
useful in the future as camouflage, being able to adapt to different
environments.




Technology :Tape measure could soon be replaced by a digital scanner
One innovation in the textile industry which could speed up the advance
of customized clothing is the digital scanner, which experts believe will
replace the tape measure within the next decade. The scanner works by
shining light on the body in a special booth and recording how light falls.
It then sends the exact shape of the body to the manufacturer to
produce clothes with exact body measurements.