Light and Shadows

Luminous objects are those which emit out their own light, e.g. sun, stars, tube light, bulb, etc., whereas non-luminous objects are those which shine by reflecting the light of the luminous objects. They do not emit their own light, e.g. moon, book and iron do not shine at all and are opaque objects.

Non-luminous objects are those which shine by reflecting the light of the luminous objects. They do not emit their own light, e.g. moon. So, it is the moon which is non-luminous.

Opaque objects form dark shadows as transparent and translucent objects allow light to pass through them.

Non-luminous objects are those which shine by reflecting the light of the luminous objects. They do not emit their own light, e.g. moon.

Whenever an opaque object is kept in the path of the light, it forms a dark patch behind itself. This dark patch is known as a shadow. It is always black in colour irrespective of the object colour or light colour falling on it.

When sunlight passes through the leaves of trees, we are able to see the circular images of the sun. It is the gaps in the leaves which act as a pinhole camera and produce an image of the sun.

To make a pinhole camera, we need two cardboard boxes, a ruler to measure the length to cut out the boxes, and a tracing paper which acts as a translucent screen in the camera.

The image formed by a pinhole camera is real, upside down, i.e. inverted and a clear or a sharp one (size of the pinhole should be quite small). 

A shadow is always formed by an opaque object. The shape of a shadow depends upon two factors:

1. Size of the source of light
2. Position of the source of light.
   Smaller the size of the light source, larger will be the image formed and greater is the distance between the object and the light source, lighter will be the image formed.

So, opaque objects block the path of the light.

The object, which by reflecting light cannot form images, is said to have a non-reflecting surface. Now, one can see its image in water, in spoon, iron sheet, gold or silver objects, etc. but carbon paper is an object which does not form images and have a non-reflecting surface.

So, a metal sheet is opaque in nature.

A plane mirror forms an image which is erect, regular and virtual. Also, it gives the same colour to the image as that of the object. The image is formed on the same side of the object and having the same size as that of the object. The image produced is just like the object depicting its shape, structure, size, colour, etc.

Light rays always travel in straight lines. When a light ray hits any surface, such a ray is said to be an incident ray. After hitting the surface, this ray reflects back by making an angle with the incident ray. This is known as reflection. Thus, it changes the direction of light. Conduction is the phenomenon to allow the passage of heat or current through an object and insulation refers to resisting the flow of heat or current through the object; transparency refers to the property of an object to allow light to pass through it.

So, a glass pane is not translucent in nature.