Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: How we see light reflecting from objects.

Learn more physics!

Most recent answer: 01/24/2013
Q:
if we see an object because of light from the source hitting the surface of the object make its electrons to excite to higher orbits and comming back to same orbit emiting a photon which strikes our eyes, then according to this, at one INSTANT of TIME, an excited electron can emit only one photon and similarly if the object contained (for example) ten electrons on its surface, only ten photons can come form that object at that instant of time and all those photons will have 3 degree of freedom to move in any direction.IF this is the case, we coudnt see a complete object at a given instant of time as all the photons emitted from that object woudnt have striken to our eyes and similarly, if 3 people are watching the same object, at a given instant of time, each person would have seen a part of that object as one electron emitts only one photon at that instant of time.... but this is not the case in real world....how is it?
- V.Praveen Kumar (age 20)
Hassan,Karnataka,INDIA
A:

Our eyes are not infinitely fast, so it doesn't matter what happens in each instant in time; rather, the eye averages over several tens of milliseconds, many orders of magnitude slower than most atomic transition rates. Furthermore, macroscopic objects have roughly 10^23 = 100,000,000,000,000,000,000,000 electrons in just a few grams of the substance. Therefore, millions of photons can be emitted each second in all directions, and our eyes will see a whole object no matter what angle we look at it from.

For very small objects (i.e. with just 10 electrons), we would need a microscope and a camera whose shutter could stay open for a long time to collect enough photons to get a decent image. In fact, various have demonstrated this by taking photographs of single atoms using optical devices! (Note that since atomic features are smaller than the imaging light's wavelength, the pictures are very blurry and don't show any details of the atomic structure.)

David Schmid


(published on 01/24/2013)

Follow-up on this answer.