# Light ( Physics)

Light . Electromagnetic radiation, very necessary in the life of living beings .

## Summary

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• 1 Electromagnetic spectrum
• 2 Propagation
• 3 Light and matter
• 4 eclipses
• 5 Reflection and refraction
• 1 Refraction
• 6 Examples
• 8 Sources

## Electromagnetic spectrum

Light is part of the electromagnetic spectrum that includes different types of waves such as cosmic rays , gamma rays , ultraviolet , infrared, and radio or television waves, among others. Each of these wave types comprises an interval defined by a characteristic quantity that can be the wavelength or the frequency .

Light sources emit light rays that propagate in all directions and in a straight line, at great speed: in a vacuum, it travels “300,000 kilometers in a second”. When light rays pass through air , water or glass , their speed is less than in a vacuum .

## Light and matter

The material behaves in different ways when it interacts with light:

• Transparent: They allow the light to spread inside it in the same direction, so that it comes out again. Thus, sharp images are seen. Examples: Glass , air , water , alcohol , etc.
• Opaque: These materials absorb or reflect light, but do not allow it to pass through. Therefore, no images are seen through it. Examples: Wood . metals , cardboard , ceramics , etc.
• Translucent: Absorb or partially reflect light and allow part of it to spread, but diffuse it in different directions. For this reason, no sharp images are seen through it. Examples: Folio, fine cloth , onion paper , etc.

## Eclipses

They occur when the Moon is placed between the Earth and the Sun , covering its rays of light partially or totally ( eclipse of the sun ), or when it is the Earth that is placed between the Sun and the Moon, casting its shadow on the latter ( lunar eclipse ).

## Reflection and refraction

When light rays, which propagate in a straight line, collide with a body, these phenomena can occur:

• Let a part of the light bounce off the body surface and back up: the light is reflected.
• If the body is transparent or translucent, a part of the light that reaches it passes through it: the light is refracted.
• Another part of the light that reaches it is absorbed by the body, which can cause various effects, such as heating, a chemical reaction or a small electric current .

### Refraction

Light refraction

It is the change in direction that light rays experience when passing from one material medium to another, for example when passing from air to water. This causes distorted images to be seen, such as when you put a spoon in a glass of water: it looks as if it has two parts, the outside and the inside of the water.

## Examples

When the Sun’s rays strike a window, refraction predominates , while reflection reflects on a mirror .

Thanks to the reflection of light we can see objects that do not have their own light, since the light rays that hit the object are reflected in it and reach our eyes.

The clearest examples we have are when we look at the Moon, which has no light of its own, but reflects the light that comes from the Sun, or when looking at itself in a mirror: light rays are reflected first in the body and then in the body. mirror, allowing vision . However, in the dark you cannot see anything in the mirror, since no ray of direct or reflected light reaches it.