Optics

# Light propagation media

Light propagating media can be opaque, translucent or transparent. When light passes through these different types of optical media, it partially undergoes the optical phenomena of transmission, refraction , absorption, reflection , etc., according to the optical characteristics of each medium.

## optical media

Any medium in which light travels can be called an optical medium. Since light is an electromagnetic waveform , it is also capable of propagating in a vacuum , and, in fact, this is the medium in which it travels with the greatest known speed, c = 299,792,458 m/s ( the symbol c is used for the speed of light ).

• ### Types of optical media

There are basically three types of optical media, they are opaque, translucent and transparent. There is no clear distinction between them, since, in any optical media, light can undergo transmission , reflection and partial absorption . Furthermore, when classifying a medium as to the propagation of light within it, we must be clear in our minds that these properties are valid for that frequency of light.

An example of this is our body, which allows a partial passage of red light. Want to take the test? Turn on your cell phone’s flashlight and cover it with your finger. You will notice that only red light is able to pass through it, in this case, since the finger is not completely transparent to red light, we say that it is translucent to it.

## opaque media

Opaque media are those that do not allow the transmission of light . When we illuminate a metal plate, for example, no portion of the light is able to pass through it, so it is an opaque medium. Realize that the opaque medium is not a dull medium, but a medium that does not allow light to pass through it.

Examples: metal, wood, plaster, cardboard, bone, etc.

## translucent media

Translucent media are those in which light can be transmitted. In these media, light is partially absorbed, in addition, when we look through them, we can see the silhouette of objects, however, we do not see them with definition. In translucent media, the passage of light is irregular , that is, the light emanating from them has different directions from the light rays that fall on them.

Examples: fog, tracing paper, etc.

## transparent media

Transparent optical media are those in which light can be transmitted with little or no absorption (in the case of a vacuum). In these media, almost all light is transmitted and we see objects with great ease. Furthermore, when light passes through a transparent medium, its path remains regular.

Examples: air, some types of glass, pure water, etc.

See also: Electromagnetic spectrum – what it is, what it means and how it works

## Exercises on means of propagation of light

Question 1) (IFCE) Consider the following statements.

I. Transparent media are media in which light travels through them in well-defined paths, that is, light passes through these media regularly.

II. In translucent media, light does not propagate. These media absorb and reflect this light, and the absorbed light is transformed into other forms of energy.

III. In opaque media, light does not pass through them as easily as in transparent media: its trajectory is not regular.

Is(are) true:

a) I only
b) II only
c) III only
d) I and III
e) II and III

Template: Letter A

Resolution:

Let’s analyze the alternatives:

I – TRUE
II – FALSE: Light does not propagate only in opaque media.
III – FALSE: The path of light is not regular in translucent media.

Question 2) (UEL) Consider the following statements:

I- Pure water is a translucent medium.
II- Frosted glass is an opaque medium.
III- Air is a transparent medium.

For the above statements, choose the correct alternative.

a) Only statement I is true.
b) Only statement II is true.
c) Only statement III is true.
d) Only statements I and III are true.
e) Only statements II and III are true.

Template: Letter C