Unit 1 : Energy Lesson 1 : light
Light :
A form of energy that affects eye causing the sense of seeing (vision )
Difference between light energy and other forms of energy :
Lightenergy differ than other kinds of energy
Because :
It is visible energy .
Sources of light :
1. The Sun :
The main source of light on earth's surface
2. The moon :
Moon's light is a reflection of sunlight that falls on its surface .
Visible Spectrum :
Light energy which can be seen by the eye
Travel of light
v Light travels in straight lines .
Example :
The Straight line :
is The path
1.Which is taken by light rays coming from the car torch .
2.Which is taken by beam of sun rays coming from the sun and passes through a narrow hole of a window or a dark room
Activity prove that :
Light travels in straight lines
Tools : lighted candle – straight cylinder of length 50 cm
Steps :
1.Fix a lighted candle vertically
2.Put one of the 2 ends of the straight cylinder
in front of the candle flame
3.Look at the flame of the candle .
Observation :
You can see the flame
4.Bend the cylinder (not straight )
5.Try to look at the candle flame through the bent cylinder
Observation :
You can't see the flame.
Conclusion :
Light travels in straight lines
Activity prove that :
Light travels in straight lines
Tools :lighted candle – 3 cardboard screens
Steps :
1.Bring 3 pieces of cardboard , each containing a hole .
2.Put them in a row in front of a lighted candle .
Where all holes and the flame are on one straight line .
3.Look to the candle flame through the hole of the last pieces of cardboard .
Observation :
You can see the flame
4.Move any of the pieces of the cardboard to right or left
The 3 pieces are not on one straight line .
5.Try to see the candle flame through the hole of the last pieces of cardboard .
Observation :
You can't see the flame .
Conclusion :
Light travels in straight lines
Phenomena happen due to traveling the light in straight lines :
1.Formation of images through narrow holes
2.Formation of shadows
Formation of images through narrow holes :
When light travels through narrow holes :
An inverted image is formed is formed
It leads to :
Designing of photographic camera .
Activity proves that :
Light travels through narrow holes forming An inverted image :
Steps :
1.Bring a cardboard ( metallic ) box opened from on side .
2.Cover the open side by a semi-transparent paper (white balloon )
3.Make a small hole on the opposite side of the box.
In a dark room :
4.Move a lighted candle in front of the small hole
of the cardboard box Until an inverted is formed .
Observation :
An inverted image for the candle is formed
Conclusion :
Light travels through narrow holes in straight lines forming An inverted image .
v This activity is the base of idea of the camera
v This box is called pin-hole camera