# The Naked Scientists Forum

### Author Topic: QED  (Read 951 times)

#### PAOLO137

• Jr. Member
• Posts: 32
##### QED
« on: 01/08/2013 09:14:43 »
I know that every sientist reccomends not to try to figure out quantum phenomena uslng our usual sensorial experience because our brain is made from the beginning and during its development to understand the macroscopic newtonian world that surrounds us. But the temptation to do otherwise is very strong (think the idea Niels Bohr made for his planetary atom). Now I am trying to "see"  this simple phenomenon:
an electron is crossing at a certain speed the space between two metal plates charged respectively + and - . an electric field in the classical definition. The electron will follow (I believe) a trajectory which is a parabola. Theory says that one of the metal plates will be shooting photons to the electron. Is it a correct imaginary view ? Thank you, PAOLO.

#### evan_au

• Neilep Level Member
• Posts: 4105
• Thanked: 245 times
##### Re: QED
« Reply #1 on: 01/08/2013 10:33:37 »
I am assuming that the apparatus is in a vacuum, otherwise the electron would suffer repeated collisions with air molecules.

The electron will follow the path of steepest voltage gradient towards the +ve plate. The trajectory will be affected by the geometry of the electrodes. But assuming the electrodes are parallel flat plates, with the electron released near the center of the negative plate, the electron will follow a straight line to the center of the positive plate.

If you graphed the position of the electron against time, the graph would take the shape of a parabolic arc.
If you started the electron near the center of the positive plate, with an initial velocity towards the negative plate, this graph would look like a parabola, reversing direction before plunging back to the positive plate.

Finally, if you started the electron with an initial velocity parallel to the plates, the electron would follow a parabolic path.

All of these paths involve acceleration of the electron, and accelerating a charge results in emission of photons.

There is another problem with this experiment - Heisenberg's uncertainty principle says that if you try to measure the position of the electron with a very fine resolution, you will severely disturb the very position and trajectory you are trying to measure.

#### The Naked Scientists Forum

##### Re: QED
« Reply #1 on: 01/08/2013 10:33:37 »