UNIT 6 NATURAL SCIENCE: LIGHT

WHAT IS LIGHT?

Light energy is emitted by light sources, such as stars, light bulbs and candles. It is the energy used by plants to perform photosynthesis and the energy that allows us to see everything around us.

Light may come from:

• NATURAL SOURCES: like the sun and other stars or fire. Some animals like fireflies, glow worms and deep sea fish, can also emit light.
• MAN-MADE SOURCES: like light bulbs, candles and laser beams.

COMPOSITION OF LIGHT

Isaac Newton discovered that white light (sunlight) is made up of different colours: red, orange, yellow, green, blue, indigo and violet. For this reason when the sun shines and it rains at the same time, we see the rainbow.

PROPERTIES OF LIGHT

The main properties of light are:

• Light travels at 300,000 kilometers per second. It is the fastest thing in the universe. For example: the light from the sun reaches the Earth in only 8 minutes.
• Light travels in a straight line.
• Ligth travesl in all directions.

LIGHT AND OBJECTS

REFLECTION AND REFRACTION

• REFLECTION: when light hits an object, it bounces off the object and changes direction. This is called reflection.
• REFRACTION: when light passes from one material to another material with a different density, it bends. This is called refraction.

THE COLOUR OF OBJECTS

When light reaches an object, some of the colours of light are absorbed, and other are reflected. For example, when we see a blue object, it appears blue because it absorbs all other colours of light and refelcts blue.

• White objects: don't absorb any colour of light, they reflect all light.
• Black objects: absorb all colours of light, they don't reflect any light.