Posted by Shiela on Friday, February 25, 2011 at 4:22pm.
Look up Gauss's law
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gaulaw.html
Do it with a sphere with charge at the center and a radius of 0.400 m
Note - Surface area of sphere = (4/3) pi r^2
Oh wow, look at this:
http://academicearth.org/lectures/electric-flux-and-gauss-law
I took that course in that room in 1957 !
area = 4 pi r^2
Thanks for your assistance-I'm not sure still how to set it up but I'm going to go to those webiste and investigate it-
The idea is that for a sphere the field is constant over the surface if the charge is considered at the center.
Therefore E is proportional to charge/(4 pi r^2)
Electric field
To help visualize how a charge, or a collection of charges, influences the region around it, the concept of an electric field is used. The electric field E is analogous to g, which we called the acceleration due to gravity but which is really the gravitational field. Everything we learned about gravity, and how masses respond to gravitational forces, can help us understand how electric charges respond to electric forces.
The electric field a distance r away from a point charge Q is given by:
Electric field from a point charge : E = k Q / r2
The electric field from a positive charge points away from the charge; the electric field from a negative charge points toward the charge. Like the electric force, the electric field E is a vector. If the electric field at a particular point is known, the force a charge q experiences when it is placed at that point is given by :
F = qE
If q is positive, the force is in the same direction as the field; if q is negative, the force is in the opposite direction as the field.
k = 1/(4 pi eo)
= 9 * 10^9 N m^2/C^2
Would I use this: E=kQ/r^2
and then I rearrange it and I have-Q=(2.95 *10^6N/C)(0.400m)^2/(8.988 * 10^9n*m^2/C^2)
=5.25E13
Is that even close?
3*10^6 * .16 / 10^10 = .5 * 10^-4
10^6/10^9 = 10^-3, I suspect you added
Note - I only carried one significant figure, doing in my head
Get it ?
Thanks-I think I'm beginning to get it-we just started this in class yesterday and I was trying to do the work due next week-thanks for your patience and explanations-I really appreciate it
Great, good luck !
Thank you very much!!