Electromagnetic Questions :) Hello everybody. I have some questions that puzzled me in Electromagnetics. I tried to answer them all , some my answers make sene some not. I hope someone hear can help . Q)If a material has a large permittivity, with it also follow that it will have a large conductivity ? Why or Why not ? A)If the permittivity constant is larger since J=sigma.E so sigma=J/E so, If E is large then sigma will be large also. I think this is wrong too. Q)Which takes more energy to construct: a solid, uniform sphere of charge or a hollow uniform spherical shell with the same diamter and charge ? Why ? (think in terms of Energy density) A) In terms of density a hollow uniformly sphere of charge will take more energy to construct. I think becasue it has longer charge density than the solid sphere. the charge in the solid sphere is spread out within the solid spheere (more space for the charge) wich will be less charge density, the charge will be more compacted and highly dense in hollow sphere, becasue of less room for charge to (spread out) My answer is wrong, I think I need to think in terms of Energy Density=1/2 DE , becasue my professor said its not the hollow. Q) You have been placed in a room with a weightless point charge ans sensitive measuring devices. How could you use this charge to determine E and B fields at an arbitrary point in the room ? A)With a test point charge I Wouild begin with Lorentz Force Law which states: F=Q(E+u x B) Determine E: Since E=Fe/Q I would measure the force on Q(the test charge) This measurement would yield E. Determine B: Since Fm=Qu x B I Would be looking at Q still, but this time I would more it at a velocity (u) and measure the force that is acting upon test charge (Q). B will be yielded operationally by undoing the cross product(how?????) . What velocity should I choose ?