Measuring Electric Field of Something

[sYanGchronize]

In many equations, I see the term E, but I'm really confused on how exactly I can calculate this value. So if I were to an experiment and I needed to find the polarization density, and I needed the E value, where can I find it?

Thanks :D

 

[dgOnPhys]

In electrostatics, the operative definition of electric field in a point P in space defines E through the force F acting on a probe charge q (placed at P), small enough that it will not alter the distribution of the sources of the original field:
E=F/q

Not sure how practical is to do this in an actual experiment, in particular you won't be able to use this definition to measure the field in close proximity to its sources unless you can constraint all charges in place. One can still try to subtract the effect of the probe charge but that's another story...

 

[cosmicraj]

Watch ,MIT OCW lectures by Walter Lewin

http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/video-lectures/

 

[sYanGchronize]

Yea, those lectures are the best. I don't know, I can probably find the charge on some website, but then, I would still have to find F. So would I then be able to use Coulomb's Law to find the force using the two known charges?

 

[cosmicraj]

Yea, those lectures are the best. I don't know, I can probably find the charge on some website, but then, I would still have to find F. So would I then be able to use Coulomb's Law to find the force using the two known charges?

See the Electrostatic Force can apply for any two point charges

 

[johng23]

You can't measure an absolute value for the polarization density, you can only measure a change in polarization. The internal field in your sample depends on the applied field and the magnitude of the polarization, since the polarization serves to decrease the field felt by the individual atoms. Since you can't measure the polarization exactly, you can not measure the field felt by individual atoms at all, so I think it is useless to try to think about a test charge in that material. What you need to do is calculate the field you are applying, based on whatever experimental parameters you are using to apply it. So if you are applying a voltage, just calculate the field in V/m...I think that's the best you can do.