Can anyone please explain to me why the following phenomena happens ?:

 

When a video projector projects an image on a mirror screen, the image that we see on the mirror, seems to originate from inside the mirror, at a depth inside the mirror which equals the distance between the projector and mirror.

 

On the other hand, when a video projector projects an image on a projection screen (which could be a white wall), we see the same image as with the mirror, only this time it does not seem to originate from within the wall, rather it seems to originate from the surface of the wall.

 

Why is there a difference between these two situations ?. Are the microscopic events that lead to the image formation, different between the mirror and white wall ?.

 

For the white wall, I know that each photon that hit a molecule of the white wall, gets absorbed, shifts an electron to a higher orbital, the electron is unstable at this higher orbital, and when it goes back to the lower orbital, it ejects a photon back. As far as I know, this is the explanation for why the white wall reflects light, and allow us to use it as a screen for the projector.

 

Is this same explanation correct for what happens with the mirror ?. If so, why is there such a differenece between the image that is created by the mirror, and the one which is created by the white wall ?.

 

Thank you very much for your help.

The difference is not in the atomic mechanics of the screen, it is in the way the light has been manipulated beforehand. There are two types of images in optics, real and virtual.

 

What you see on a screen is a real image. All of the light rays (if you do ray-tracing) from each point of the object will reconverge at one point on the image. Anyone can look at the screen and they will see the same thing.

 

What you see in a mirror is a virtual image; the image you see cannot p be projected onto a screem since it does not come from a one-to-one mapping of light rays from the object to the image. What you see in the mirror depends on where you stand.

 

http://www.colorado.edu/physics/phys1230/phys1230_fa01/topic18.html

http://www.pa.msu.edu/courses/2000spring/PHY232/lectures/lenses/images.html

All of the light rays (if you do ray-tracing) from each point of the object will reconverge at one point on the image.

 

So all of the light which is coming from a certain (x,y) point on the object's plane, will reconverge at a certain unique (x,y) point on the screen ?.

 

But why doesn't it happen when the screen is a mirror ?.

So all of the light which is coming from a certain (x,y) point on the object's plane, will reconverge at a certain unique (x,y) point on the screen ?.

 

But why doesn't it happen when the screen is a mirror ?.

 

Light from a plane mirror (striking different points on the mirror) doesn't converge, it reflects at the same angle it strikes.