All light comes from atoms, tiny particles that make up everything in our universe. When atoms gain energy they give it off as light. An atom that has such energy is called excited.
Some light is natural , like sunlight or light from stars . Other light is produced from things people make, like lamps or flashlights. A light bulb glows because electricity heats a wire inside. Candles produce light from fire when you light them. Lasers are devices that produce powerful beams of light in which all particles have the same energy and travel in the same direction.
There are certain substances that glow in the dark. Their atoms are excited for a certain time and after that they release light. Some insects, like fireflies glow naturally.
For a long time scientists were not sure about how light travels through space. Some thought that light behaves like a wave, others claimed that light particles travel in a straight line. Today, scientists agree that light is an electromagnetic wave made up of electrical and magnetic forces that travel through space at a very high speed. However, light is also a stream of particles called photons, which travel like a beam.
Light waves can be compared to waves in water. They have a wavelength, frequency and amplitude. The wavelength is the distance between the two highest parts of a wave, the frequency is the number of times that a wave passes a certain point every second, and the amplitude is the distance between the highest and lowest points of a wave.
When light waves strike an object three things may happen. The light can be reflected, absorbed or it may change its direction.
What happens to light depends on the kind of object or material that it hits. Transparent objects, like glass, let light waves pass through without mixing them up. You can see through this material. Translucent material also allows rays to pass through, but it mixes them up so that you cannot see through such objects clearly. Opaque materials don’t let any light pass through.
Most objects do not produce their own light. You can see these objects because light from the sun or from a lamp bounces off them and then travels to your eyes.
Some objects reflect little light, others, like mirrors or water reflect almost all the light because they are smooth and flat. The rays bounce off in only one direction. Reflected light also makes things sparkle and shine. When light shines on a normal object, like a tree, the rays bounce off in many directions.
When light passes through an object it slows down because the molecules of a solid object are more densely packed than air molecules. It also changes its direction of travel – it refracts.
Example: Swimming pools do not look as deep as they really are because of the way light is bent. Water slows light down by about 25 per cent and glass slows it down even more. Light waves bend towards the glass, slow down and behind the glass resume their normal speed.
Another example is picking up a stone in water. The stone is not where you think it is. It appears to be farther away than it really is
You must be logged in to post a comment.