5th Class Science Lights, Sound and Force Light and Sound

Light and Sound

Light

Light is a form of energy which enables us to see an object. Sun is the main source of light on our earth.

Sun

Luminous Objects

Sun, candle, diya and lamp are examples of objects that produce light. These are called Iuminous objects.

Diya                                                                 Lamp

Non luminous Objects

The objects that do not produce Tight are called non-luminous objects. Paper, kite and table are examples of non-luminous objects.

Paper                                       Kite                                    Table

Shadow      

Light always travels in a straight line. When there is some obstruction in the path of light, we see a shadow. Light is always needed for a shadow to form. Shadows always form on the opposite side of the source of light. Shadows can never form in total darkness. Some objects cast dark shadows while some cast faint shadows.

Sometimes shadows are smaller, and sometimes they are bigger than the actual size. Long shadows are formed in the morning and the evening. Short shadow is formed at noon.

Opaque Objects

Wood and metal are examples of opaque objects. No light can pass through such objects. So they form clear and dark shadows when they are placed in front of a source of light.

Transparent Objects

These objects allow almost all light to pass through them. So transparent objects form very faint shadows (or no shadow at all). Plain glass is an example of a transparent object.

Translucent Objects

Butter paper is an example of a translucent object. Such objects block only a part of the light that passes through them. So they throw a faint shadow.

Sound

A wave of vibrations that spreads from its source. Vibration is the back-and-forth motion of an object.

Sound is produced when we talk, when we strike a steel tumbler with a spoon. Our tongue helps us to make sound. Some sounds are soft, some are loud.

Some sounds are pleasant and some are unpleasant.

Noise

Sound that is loud and unpleasant is called noise. Too much of noise is harmful for our health. Therefore, we should speak softly. We should play television, music system, etc. in low volume so as not to disturb our family and neighbours.