errwrsysalan one year ago @theEric @PsiSquared @Vincent-Lyon.Fr About diffuse reflection First, check my understanding please: http://www.physicsclassroom.com/Class/refln/u13l1d6.gif As shown in the diagram, I am sure that it will still follow the law of reflection but light will be reflected back from all different directions as the all the normals have different angle and photon is infinite small which means a beam of light will have infinite number of photons. Therefore, we will see the image no matter from what direction. Am I right so far? If not, please correct me.

1. errwrsysalan

Sorry, I can't type too much so I am going to type the questions now

2. errwrsysalan

Question : 1. If 10 people stand around an object (diffuse reflection), with a constant distance to the object. Will they see the same image if we ignore the effect of perspective? (include color, intensity, shape and so on) 2. How do we calculate the intensity of lights that are reflected? What information do we need to know? 3. If they all see the same image (question 1) and I want the calculate the light for all direction. Does it mean I can choose a group of light from a random direction and copy this group of light for other directions?

3. errwrsysalan

Well. I just tried to look at an object from all direction (question 1), it looks almost the same but some area will have different intensity if I change my viewpoint. What cause this? Does it mean I need to calculate for all directions (question 3)?

4. errwrsysalan

Questions: 4. Usually if we want to calculate the whole image that will be formed, do we do it by separate a beam of light into single light rays and do the calculation? Or is there any better method? 5. If we use the method that mentioned in question 4 and we want to calculate for diffuse reflection, how small does a light ray need to be? We can't even really see the roughness with our eyes unless we use microscope.

5. theEric

Hi! I'm not really the one to answer these, but I'll say something in the absence of smart people! Firstly, I found a flaw in your theory, which is good! That's how learning works. There are not infinite photons, so just remember that! They are often described as "packets of energy." And each photon has a real amount of energy. So infinite photons would mean infinite energy! Just more of a side note: Photons are "packets of energy," because they each have a specific amount of energy. I don't know if you've learned this, but \(E=hf\). Here, \(h\) is a constant and \(f\) is the frequency (another constant). For number one, I think that the situation is idealized. Like, maybe the light is evenly spread. If all ten people are the same distance away, the intensity would be the same. The color would be the same, since the frequency of reflected light will be the same. However, if the light was directed light, there would be a shadow that some people would see and some people wouldn't. Good luck!

6. douglaswinslowcooper

I could not connect, but diffuse reflection is very different from reflection from a mirror surface. Diffuse reflection is like reflection from frosted glass and will not give you an image, though the light may be somewhat more intense in the direction where the angle of reflection equals the angle of incidence.

7. errwrsysalan

When we say two waves are coherent, do we also refer that they have same amplitude?

8. errwrsysalan

6. When we say two waves are coherent, do we also refer that they have same amplitude? 7. I found polarization of light hard to understand. How could a light ray have secondary direction? It is a line, not a plane. Though I know light is lots of wave and we can convert it into a plane but isn't there any method to deal with polarization of light with light ray?

9. errwrsysalan

8. What is the different between scattering and diffuse reflection? 9. Isn't thin films interference just reflection? Is there any interference? 10. There are many types of scattering. If I want to run a simulation for real world, do i need to simulate all types of scattering?

10. errwrsysalan

@PsiSquared @Vincent-Lyon.Fr Come on men= =I need help

11. douglaswinslowcooper

coherent waves are in phase with each other, though not necessarily of same amplitude.

12. douglaswinslowcooper

real world simulations should include both specular and diffuse scattering

13. douglaswinslowcooper

Thin-film interference has constructive and destructive addition of waves from top and bottom surfaces of the thin film region.

14. PsiSquared

@errwrsysalan, as far as diffuse reflection, as the reflection gets more diffuse, the ability to form an image goes down because information from the object, i.e. light from each point on the object, will be diffused in many directions and will be lost. A very lightly diffuse surface could very well reflect an image, but such an image will be dimmer (less light) and blurrier (information about each object point will be spread out and won't come to a focus.

15. PsiSquared

16. PsiSquared

@errwrsysalan, to calculate the intensity of light off of a diffuse surface, you have to know the angle of the surface to the incoming light, surface properties (a function that defines the surface's diffusion), and the angle of the surface to the person viewing the surface. From that calculations can be made, although said calculations won't be exact. Note this is standard operating procedure in a field of optics called radiometry: http://en.wikipedia.org/wiki/Radiometry . Knowing things such as the diffusion of a surface is very important when doing things like calibrating satellite sensors for satellites that study Earth.......or even other planets.

17. PsiSquared

@errwrsysalan, I just sent you an FB friend request. I'm in the US, but as it happens I've got a best friendp--a tall, ugly fellow--in one of Auckland's suburbs, Balmoral.