Need some Electromagnetics help!! (simple stuff)

[heat23]

yeah our homework assigment comes from a different book than ours. and our book doesnt explain anything...so i need some help...

1)Eight 25-nC point charges in free space are located symmetrically on a circle of radius 0.2 m centered at the origin in the z=0 plane. (a) At what point on the z axis is [the magnitude of] E a maximum?? (b) What is [maximum value of] E??

for (a) im thinkin the answer is either 0 or .2. but i dunno



2) The circular regtion, p(RO) < a, z=0, carries a uniform surface charge density ps(RO sub S). Find E (vector) at P(0,0,h), h > 0


no idea ha


if anyone knows any good tutorial websites..lmk

thanks in advance

 

[Ameesh]

its been a while but..


#1 : i believe it would be at .2 because if it was in the middle of the cirlce allt he charges would cancel each other out (use vectors)


#2 : use the right hand rule.


gladd you got elite

 

[heat23]

ok thanks..
then for 1b) how would i calculate the max value??

and for 2) how do i use the right hand rule

 

[Ameesh]

use a sum of vectors for the charges of each point charge for #1 and2 take your right hand and curl your fingers in the direction of the current and your thumb will point in the way the force is going.

 

[iamwiz82]

always use your right hand!! left hand will give you the exact opposite answer. I'm speaking from experience!