Light is a form of energy which helps us in seeing objects. When light falls on an object, some of the light gets reflected. The reflected light comes to our eyes and we are able to see an object.
Sources of Light
A body which emits light by itself. It can be natural like sun or artificial like electric bulb.
A body which does not emits light by itself.
If we are able to see clearly through an object, it is said to be transparent like water, glass
If we are able to see not clearly through an object, it is said to be translucent like butter paper
If we cannot see through an object at all, it is an opaque object like wood
Formation of shadows
When an opaque object is placed in path of light, a dark portion is formed on the opposite side of object on the screen. This dark portion is shadow.
(1) The size of shadow depends on the distance of source of light and on the angle at which the light rays fall on the object.
(2) If the source of light is closer to the object, a larger shadow is formed than when the source of light is far from the object.
(3) The shadow can be seen only on a screen. The ground, walls of the rooms, a building, or other such surfaces act as a screen for the shadows you observe in everyday life
(4) Shadows sometimes gives lot of information about the object.
(5) Shadows are in black in colour and this is not changed by the colour of the opaque objects. So a red and yellow rose will have same black shadows.
A Pin-Hole Camera
How to prepare it
(1) Take two boxes so that one can slide into another with no gap in between them. Cut open one side of each box.
(2) On the opposite face of the larger box, make a small hole in the middle.
(3) In the smaller box, cut out from the middle a square with a side of about 5 to 6 cm.
(4) Cover this open square in the box with tracing paper (translucent screen).
(5) Slide the smaller box inside the larger one with the hole, in such a way that the side with the tracing paper is inside
Now it is ready to use How to use it
(1) Hold the pin hole camera look through the open face of the smaller box. You should use a piece of black cloth to cover your head and the pinhole camera.
(2) Now focus on the object you want to capture in the camera.Make sure that the objects you wish to look at through your pinhole camera are in bright sun shine.
(3) Move the smaller box forward or backward till you get a picture on the tracing paper pasted at the other end
How the Images looks like pin-hole camera?
Upside down (inverted) images are formed. Image in a pin hole camera is real , inverted and smaller in size.
Natural Pin-hole Camera
When we pass under a tree covered with large number of leaves, we notice that small patches of sun light under it. These circular images are, in fact, pin hole images of the Sun. The gaps between the leaves, act as the pin holes. These gaps are all kinds of irregular shapes, but, we can see circular images of the Sun. This is called Natural Pin-Hole Camera
Rectilinear Propagation of Light
Light travels in the straight line and this is called rectilinear propagation of light
Two important terms in this regard
(1) Ray of Light: It is the path along which light travels in the given direction. Now as we know light travels in the straight line. We can represent ray of light by straight line with direction arrow
(2) Beam of light: A bunch of ray of light in the given direction
We all have seen the plane mirror. It is very commonly used in our life. We used that in the car, dressing room etc. Plane mirror are formed by layering molten aluminium or silver onto the back of a sheet of glass inside a vacuum
Reflection of Light
We see our face in the Mirror. This is possible through the phenomenon Reflection of light. Basically Light rays reflected from parts of our body fall on mirror and are reflected back. When these reflected rays reach our eyes (reflected on our retina), we can see the image in the mirror.
So reflection of light is changing the direction of the light. Image formation by Plane Mirror
The image formed is erect, same size and laterally inverted. It retains the same colour as the object Lateral Inversion
The right side of the object appears to be the left side of its image and vice-versa
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