35. Light
How is light formed?
Heat produces light. The most important source of light on planet Earth is the central star of our solar system, the Sun. The Sun is extremely hot. This temperature is the result of the radiation produced in nuclear reactions that take place inside the Sun.
Light radiation can travel through empty space. It moves quickly, at a speed of 300 000 kilometers per second.
Although the Sun is located over 150 million kilometers from Earth, its light reaches our planet in approximately eight minutes!
Lighting.
Electricity can also produce light, for example by heating different materials. Lightning is a natural source of electric light caused by electric charges that are discharged.
Many living organisms can also produce light without producing heat.
The picture on the right displays a computer model of an anglerfish, which produces light with a special organ.
An anglerfish.
Some other animals, such as fireflies, can also produce light.
Cold light can also be produced in chemical reactions. An example of this is glow sticks. When the capsule inside the glow stick is broken, the two substances inside the stick can interact with one another. Their reaction produces light.
Glow stick bracelets.
How does light travel?
Light travels directly. This is why shadows are formed. If light could move freely, it could easily travel behind shadow-producing objects. The image on the top left shows the Sun, the Moon and the Earth. The shadow produced by the Moon has produced a solar eclipse. This means that the Sun is completely blocked out in certain places on the Earth.
The image on the bottom left shows the Sun, the Earth and the Moon. If you were to look at the Sun from the Moon, you would see that it is blocked by the Sun. In other words, the Moon has ended up in Earth's shadow. This has produced a lunar eclipse.
Light reflects
During bright moonlit nights, the Moon reflects sunlight so well that you can see around yourself even without a flashlight.
The function of the reflecting telescope is based on the reflection of light. It contains a round, concave mirror that magnifies the image, whereas another mirror reflects the image into the telescope's ocular.
Reflecting telescopes are used to study the solar system and the universe. The world's largest reflecting telescope is found in the Canary Isles. Its mirror is 10,2 meters wide.
Concave and convex mirrors
Almost all surfaces reflect light. The sensor cells of our eyes sense this light and process the visual information. The flatter and whiter the surface is, the more light it reflects. For example, a mirror reflects light well because its surface is extremely flat and has a metallic white color.
There are different kinds of mirrors. Some mirrors magnify the objects in the mirror, whereas other mirrors reduce the size of the objects in it. These phenomena can be influenced by changing the shape of the mirror.
Concave mirrors magnify the objects reflected by it. For example, a pot lid can act as a concave mirror. Concave mirrors are used in telescopes and binoculars. They are also used when applying makeup or shaving.
When a pot lid is turned upside down, the result is a convex mirror. Convex mirrors reduce the size of the objects reflected in it. They are used in dangerous crossings and in cars.
Light refracts
When light travels from one substance through another, it refracts.
The refraction of light can cause illusions. For example, the refraction can cause an object to seem larger than it actually is.
Strong refractions are created with lenses, which can be made from glass or plastic. A concave lense collects the rays of light into one place, as seen in the image on the left below. A convex lense spreads the rays of light in different directions, as seen in the image on the right below.
Making use of refraction
The refraction of light is used in many kinds of tools.
A magnifying glass is a type of concave lens, which makes objects seem bigger than they actually are.
A microscope contains several lenses that form an objective. Things that placed in the microscope are viewed through the ocular, which is used to focus the image reflected through the objective. Microscopes can be used to see and study things that we cannot distinguish with the naked eye, such as cells and bacteria.
Lens telescopes also make use of refraction. A lens telescope contains several lenses. A lens telescopes can be used to study stars and planets.
Splitting light
By refracting light strongly, it can be split into its constituent wavelengths or spectre.
A glass that is used to refract light in order to create spectres is known as a prism.
In nature, drops of water can act as prisms. This is how rainbows are formed. Spectres can also form near waterfalls or even sprinklers.
Terminology
| Term | Explanation |
|---|---|
| relfection | A process where radiation changes its direction when hitting an object. |