Light is the form of energy which makes things visible to us. Some objects emit light while others lack this property and hinder its path to cast shadow. On the basis of this property different objects can be classified into:
- Luminous objects: Objects that can emit light on their own are known as luminous objects. For example: sun, bulb etc.
- Non- luminous objects: Objects that cannot emit light on their own are known as non-luminous objects. However these objects are visible due to light falling on them. For example: moon, earth, chair etc.
- Transparent objects: Objects which allow light to pass through them completely are termed as transparent objects. For example: glass, air etc.
- Translucent objects: Objects which allow only some part of light to pass through them are termed as translucent objects. For example: tissue paper, butter paper etc.
- Opaque objects: Objects which do not allow any part of light to pass through them are known as opaque objects. For example: table, book, chair etc.
Whenever light falls on an opaque object a dark region is formed behind the object. This region is termed as shadow. Translucent objects produce a weak shadow whereas transparent objects do not cast any shadow.
Eclipse: A phenomenon by which either the sun or the moon becomes invisible to us for some time due to the formation of shadow of one over another is termed as eclipse.
Pinhole camera: A pinhole camera is basically an arrangement of cardboards with a pin hole in order to form the image. It can be seen as a camera without lens.
- Construction of a pinhole camera:
- Take two boxes of different sizes such that one can slide over another with no gap in between them.
- Cut open one of the face of each box. On the opposite face of the larger box, make a pin hole in the middle.
- From the smaller box, cut out a square with a side of about 4 to 5 cm from the middle. Use tracing paper or other translucent material to cover this open square in the box.
- Force the smaller box into the larger one such that the side with the hole in larger box and the side with the tracing paper in the smaller box are on same side (inside) as shown in the figure.
- When seen through the pinhole on an object, an image is observed on the tracing paper.
- The image formed is inverted in nature.
Properties of light:
- Light always travels in a straight line.
- When a ray of light falls upon an opaque object, it bounces back. This phenomenon of bouncing back of ray of light is termed as reflection of light.
Thus we have discussed about some implications of light on shadows and its reflection to a considerable extent. Students who wish to apply what they have learned could do so by working on some sample questions and answers like the one provided here- NCERT solutions for light.