Points to Remember

Points to remember
1.    Source of light: An object which emits light, is called a source of light. For example, sun, torch, etc.
2.    Non-luminous objects: These are the objects which do not emit light of their own. Such a body becomes visible when light falls on it. For example, the moon, the planets, etc.
3.    Ray of light: A straight thin beam of light from a source to an object is called a ray of light.
4.    Obstacle: An object which comes to the path of the light is called an obstacle.
5.    Formation of a shadow
    (i)     All the opaque objects seem to form a dark shadow of their own.
    (ii)     We need a source of light, an opaque object in the way, and a screen to see a shadow.
    (iii)     Screen: This is a surface on which the :shadow is formed. It maybe a butter paper or simply ground.
    (iv)     Shadows give us some information about shapes of objects.
    (v)     The colour of the opaque object does not affect the colour of the shadow. 
    (vi)     All the space behind the opaque object, up to some distance behind it seems to be filled with·the shadow.    

6.    Image formed by a pinhole camera
    (i)    Images formed by a pinhole camera are upside down. Here is a picture showmg the path of rays of light coming from an object far away to a pinhole and then to screen.    
    (ii)    When sunlight passes through the leaves of a tree, the gaps between the leaves act as the pinholes. These natural pinholes cast nice round images of the sun.

7.    Rectilinear propagation: Light travels in a straight line. It is called rectilinear propagation of light.

8.    Image formation by a plane mirror: We are able to see images through a mrrror. Image formed by a mirror (flat) has following features:
    (i)     Reflected image retains the colour of the object.
    (ii)     Image is erected but laterally inverted.

9.    Lateral inversion: Right side of the object appears as left side in the image formed by a plane mirror. For example, if we show our right hand image in the mirror will show as left hand.

10.    In a mirror, if you see another person, surely the other person can also see you in that mirror.

Keywords

1.    Luminous: Objects that give out or emit light of their own are called luminous objects.
2.    Mirror: A smooth shining surface, which rebounds the light back in same or in different directions is called a mirror.
3.    Opaque objects: If an object completely stops the passage of all the light falling on it, it is an opaque object.
4.    Pinhole camera: It is a device which forms a photograph-like image of a bright object on a screen.
5.    Reflection of light: When a ray of light falls on a smooth and polished surface, light returns back in the same medium. It is called reflection.

6.    Shadow: Opaque objects do not allow light to pass through them and cast dark patches behind them. These dark patches are called shadows.
7.   Translucent objects: Some objects allow only a part of light falling on them to pass through, such objects are called translucent objects. For example, a single thin sheet of paper.
8.    Transparent objects: Those objects which allow all the light to pass through them are called transparent objects.