05. Light and vision
The main factors that must be satisfied to have complete vision are light and the eye.
Activity
Cut a hole at the center of the lid. Cut another small hole on one side. Keep small object in the middle of the box and close the lid. Close the hole on top.
First Observe – hole at the side. identify the object by looking same hole. Second observe – Open the top hole and direct the light of the torch through the hole.
Observation
Light is needed to see something clearly.
Sources of light
The objects we use to light are known as sources of light. The main natural source of light is the sun.
We use bulbs, lamps, candles and other artificial sources to get light because there is no sunlight in the night.
Luminous object – Can produce their own light.
sun , lighted bulb, lighted lamp, glow warm, fire fly, light emitting mushrooms
Non luminous object – Objects do not emit their own light.
Moon
Transmission of light through objects
Light transmission – Solids
Activity
Cut a square of the middle of the cardboard. Light the candle. Keep the things (Metal sheet, oil paper, decorative glass, glass, polythene) in the middle of the hole to cover it.
Observation
- Glass – Light and the flame are clearly seen
- Oil papers – Light is seen but the flame is not clearly seen
- Metal – Light and flame cannot be clearly seen.
Light transmission – Liquid
Activity 5.4
Fill the bottles with liquids (water, honey, used engine oil ,soft drinks, kerosene oil ). Then light the candle and Keep the bottle.
Observation
Some liquids – Can see both the objects and the light clearly.
- Transparent objects – Can see both the objects and the light clearly
Glass , transparent colourless polythene
2. Translucent objects – Light can be seen, the objects cannot be clearly seen
Oil papers, unclear water, coloured cellophane papers
3. Opaque objects – Cannot see either the light or the object
Cardboard, wood , metal, paper, tar
Light rays and light beams
Light transmit in straight lines.
Light ray – To show a light ray , use a straight line with an arrow
Light beam – Collection of light rays. Ex – torch
Use several straight line with arrow heads to show a light beam.
Light is transmitted only in a straight line.
Activity
Make holes in the cardboard. Light the candle. Take the needle with a string and send it through the holes. Fix the string in a straight line and observe. Change the string and observe.
Observation
Light is transmitted only in a straight line.
Light rays
Activity
Keep the comb on the white paper. Direct the torch towards the comb.
Observation
Beam of light emitted by the torch and the light rays travel through the comb. (Straight lines) They are considered as light rays.
Light transmits from the torch through the smoke in the bottle
Activity
Make a hole in the cardboard and insert the joss sticks. Light the joss sticks. Let the bottle to fill with smoke and direct the laser beam torch. Change the direction of the torch and observe.
Observation
The path in which light transmit from the torch through the smoke in the bottle.
Path of the light ray through the bottle of water
Activity
Fill the bottle with the soap solution. Keep the torch near the bottle and light it. Change the direction of the torch.
Observation
Can see the path of the light ray through the bottle of water.
Applications of light
- Production of food in plants – The energy needed for the process of food production is obtained from the sunlight.(Photosynthesis)
2. Give a clear vision –
Earlier people – Sun , moon, stars
After invention of fire – Bulb
The first bulb with carbon filament in the United States of America was invented by Thomal Alva Edison in 1879.
3. Illumination – Most of the countries in the world use different coloured and patterned bulbs to illuminate various occasions.
4. Signals
Traffic light
light house – Signals to the sailors
5. Communication – Telephone – optic fibers , maintain internet connections.
6. Medical field – laser lays – eye patient , heart operations, treat wound. With the use of optic fibers, the interior parts of the body are easily observed. Equipment used to lighten the interior of the body is called the endoscope.
7. Entertainment – In musical shows and fairs , toys
Light beams of headlights could be seen through fog. The reason is that air is transparent on normal foggy conditions but air becomes translucent on foggy conditions. When the humidity is high in air, air becomes translucent.
There is a new type of lamp in modern vehicles as fog light.
Optical fibers are a type of flexible fibers which are made up of special type of glass or plastic. An optic tube is called a collection of such fibers. The use of such tubes to transport light is called optic fiber technology.
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