Does light from a point source spread out?

In summary: It sounds like you are trying to build something.In summary, your teacher was discussing the strength of a laser and how it is inversly proportional to square of the distance from the source. This is true for most lasers, but there are some exceptions.
  • #1
Alvin
6
0
I have been looking into the strenth of an infrared light source at different distances from a point source. My teacher said that the light would not spread out but when I looked on the internet i found something that said the strength was inversly proportional to square of the distance from source, which is correct and why?
 
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  • #2
You are right. Maybe your teacher talking about a laser? It doesn't follow inverse square, but it does spread out.
 
  • #3
When talking about a point source in optics it normally means that the physical size of the source of emission is very small. That means that all of the rays coming from the source originates at a "point" in space. It also means that the rays are diverging from the point source in "all" directions. I put the all in inverted commas since this is not possible in practice since the rays will normally fill only a small cone centered on the source and extending away from it. The amount of radiation from a point source will decrease according to the inverse square law with increasing distance.

Other sources of emission like lasers (and infrared lasers) also emit rays from a small region in space, but the rays coming from them are traveling parallel to each other, we say it is a collimated beam. In this case the amount of light will be constant irrespective at what distance you are from it (if you stay in line with the beam!).

Plasma lasers create their light in a tube. The rays bounce back and forth between the endpoints of the tube. The rays that are not traveling along the tube exit it along the side, while the rays traveling along the tube will eventually exit it at one of its ends thereby producing a collimated beam.

Solid state lasers emit their rays from a small region in space - the junction - the region where the semiconductor materials are joined. This will act like a point source, but normally a lens is used to collimate the rays by using a convex lens with a short focal length. The lens is positioned so that its focal point is located at the point source. This will cause the rays to be parallel on the other side of the lens. The lens need to be of such material so that it is transparent to the rays though!
http://www.repairfaq.org/sam/laserdio.htm" [Broken]
 
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  • #4
Do you no if the strength of the light follows any pattern or formula?
 
  • #5
Alvin said:
Do you no if the strength of the light follows any pattern or formula?

What do you mean by "strength of the light" ? Are you referring to intensity ?


marlon.

ps : your teacher was talking about laser light indeed.
 
  • #6
There are no conformed standards as far as the production of these devices are concerned. If you cannot get hold of the data sheet on the particular product it is best to investigate it experimentally, although finding a device that can actually measure the infrared light and setting up conditions for such a procedure might prove quite challenging! So I would opt for hunting for the data sheet if I were you. Look at the link that I inserted at the end of my post. It may answer some of your questions. Why are you interested in this property of your source?
 
  • #7
Part of a courseworky thing
 
  • #8
So they expect you to actually measure it? What do you know about the source? Producer? Product number?
 

1. What is a point source of light?

A point source of light is an object that emits light from a single, localized point in space. Examples of point sources of light include stars and light bulbs.

2. Does light from a point source spread out?

Yes, light from a point source does spread out. This is known as the phenomenon of light diffusion or light spreading. As light travels away from the point source, it becomes more spread out due to the scattering of photons in all directions.

3. How does light spread out from a point source?

Light spreads out from a point source in a process called spherical spreading. This means that the light waves travel outward from the point source in all directions, creating a spherical wavefront.

4. Does the intensity of light decrease as it spreads out from a point source?

Yes, the intensity of light decreases as it spreads out from a point source. This is because the same amount of light is being spread over a larger and larger area, leading to a decrease in the concentration of photons.

5. Can the spreading of light from a point source be observed in everyday life?

Yes, the spreading of light from a point source can be observed in everyday life. For example, if you shine a flashlight in a dark room, you can see that the light becomes less intense as it spreads out from the source. This is also why shadows appear when an object blocks a point source of light - the light is being blocked from spreading in a particular direction.

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