Bob182

google on the Dirac equation

I've added you to my msn - it'll be easier to explain that way!

I am referring to the ions yes. What occurs at the cathode when a positive ion approaches?

Yes they will conduct electricity, but the current would also be due to +ve charges and the questions ask which one will be due only to negative carriers.

The key would be to look at possible charge carriers in each of the substances. Molten NaCl comprises of Na+ and Cl- ions. Potassium Nitrate, KNO3, exists as K+ and NO3- ions in solution. Acidified water contains excess H+ ions. Aluminium has a large number of mobile electrons available to carry charge.

If you resolve your forces you will find the answer. The key to these kind of questions is that if the system is static, then the net force in any direction is zero - i.e. they cancel each other out. I suggest looking at the vertical forces and horizontal forces in turn.

yes, it is obtained from the energy/momentum invariant equation and has the value: m0 = sqrt(E^2/c^4 - p^2/c^2) it is frame independant and has the same value as the rest mass.

it's just the rest mass, i.e. what you would measure if the object was not moving with respect to you.

Are you referring to it radiating isotropically over all solid angle' date=' or isotropically throughout the electromagnetic spectra? The sun's spectra is approximately that of a black body at 5780 K (e.g. see here) As for the intensity, that of isotropic radiation will drop off as 1/r^2.

So if I were to enclose myself in a sufficient amount of lead, I would become weightless?

The speed of individual photons through a material is still c, however, electrons can absorb a photon and jump to a higher energy quantum state before re-emitting another photon. Thus light appears to travel through a material at a speed less than c, resulting in the optical effect you mentioned. Such interactions between electrons and photons are described very nicely by QED.