A solid metallic sphere of radius a carries total charge Q. No other charges are nearby. The electric field just outside its surface is keQ/a2 radially outward. At this close point, the uniformly charged surface of the sphere looks exactly like a uniform flat sheet of charge. Is the electric field here given by σ/ε0 or σ/2ε0?

σ
ε0

σ
2ε0

Question

A solid metallic sphere of radius a carries total charge Q. No other charges are nearby. The electric field just outside its surface is keQ/a2 radially outward. At this close point, the uniformly charged surface of the sphere looks exactly like a uniform flat sheet of charge. Is the electric field here given by σ/ε0 or σ/2ε0?

σ
ε0
 
σ
2ε0

jamesj · Answer

ok ... what the electric field from a (infinite) flat sheet with charge density sigma?

anonymous · Answer

its asking which one would i use to solve the problem.

jamesj · Answer

And I'm asking you what you know about the electric field from a flat conducting sheet. This is a standard result. The question is really asking you to remember which formula is for two parallel sheets, and for just one sheet. For this questions, and all the others you're asking, you'd enjoy watching this awesome lecture on the topic: http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/video-lectures/lecture-3-electric-flux-and-gausss-law/

anonymous · Answer

id use.. sigma/epsilon0?

anonymous · Answer

and i will defenitly watch the video.. I've been struggling..obviously.

jamesj · Answer

Wrong choice.  Go and watch the lecture.  He explains it well and the demonstrations are great.