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July 29, 2015

July 29, 2015

Posted by **Shiela** on Friday, February 25, 2011 at 4:22pm.

If you could just direct me with a formula-then I'll do it and check back with my answer-Thank you for you help

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 4:25pmLook up Gauss's law

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 4:26pmhttp://hyperphysics.phy-astr.gsu.edu/hbase/electric/gaulaw.html

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 4:28pmDo 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

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 4:31pmOh wow, look at this:

http://academicearth.org/lectures/electric-flux-and-gauss-law

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 4:33pmI took that course in that room in 1957 !

- surface area error -
**Damon**, Friday, February 25, 2011 at 4:34pmarea = 4 pi r^2

- Physics-Please help with formula -
**Shiela**, Friday, February 25, 2011 at 4:35pmThanks 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-

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 4:38pmThe 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)

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 4:44pmElectric 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.

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 4:47pmk = 1/(4 pi eo)

= 9 * 10^9 N m^2/C^2

- Physics-Please help with formula -
**Shiela**, Friday, February 25, 2011 at 4:48pmWould 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?

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 5:00pm3*10^6 * .16 / 10^10 = .5 * 10^-4

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 5:02pm10^6/10^9 = 10^-3, I suspect you added

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 5:03pmNote - I only carried one significant figure, doing in my head

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 5:05pmGet it ?

- Physics-Please help with formula -
**Shiela**, Friday, February 25, 2011 at 5:05pmThanks-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

- Physics-Please help with formula -
**Damon**, Friday, February 25, 2011 at 5:07pmGreat, good luck !

- Physics-Please help with formula -
**Shiela**, Friday, February 25, 2011 at 5:08pmThank you very much!!