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 Electricity and Magnetism Electricity and Magnetism Physics Help Forum Feb 24th 2015, 11:14 AM #1 Junior Member   Join Date: Feb 2015 Posts: 1 problem with potential difference (delta V) I'm asked to: b. Find the potential difference V2 - V3. Point 2 is just below the sphere, and point 3 is right beside the positive glass disk. In part A. : Find the potential difference V1 - V2. Point 1 is at the center of the plastic sphere, and point 2 is just outside the sphere. My work for part a is. e0 is 8.85e-12. Q is charge of the thin plastic shell, 1.3e-5. A = pi(4)^2, where 4m is radius of the thin spherical shell Electric Field due to cap is: E = (Q/A) / e0 E = [(1.3e-05) * (pi(4)^2)] / 8.85e-12 = 29223.4 V/m dL = radius of the plastic spherical shell, 6mm. deltaV = E * dL = (229223.4)(.006) deltaV = 175.34V but since we know that the direction of E and direction of path are in the same direction deltaV is negative. deltaV = -175.34V now for part b. d is distance from center of spherical shell to positive disk, 18mm. V2 - V3 = E * (d + .006) V2 - V3 = -672.1382V sum of deltaV = (V1-V2)+(V2-V3) = -847.4782V but this answer is wrong. It could be that I am using the formula incorrectly but we just recently used this formula to calculate deltaV for different location of source charges. Below is the attached picture of the problem   Feb 25th 2015, 12:32 PM   #2
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To get started, I found these errors:

 Originally Posted by nakenjiex My work for part a is. e0 is 8.85e-12. Q is charge of the thin plastic shell, 1.3e-5. A = pi(4)^2, where 4m is radius of the thin spherical shell
But the charge on the sphere is -5e-10, and the radius of the shell is 6 mm, not 4 mm.

 Originally Posted by nakenjiex Electric Field due to cap is: E = (Q/A) / e0 E = [(1.3e-05) * (pi(4)^2)] / 8.85e-12 = 29223.4 V/m
This should be E = -5e-10/(4 pi(0.006)^2)/8.85e-12 = -1.25e+5 V/m.

See if this helps get you on the right track.

Last edited by ChipB; Feb 25th 2015 at 12:34 PM.  Tags delta, difference, potential, problem Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post gokul Electricity and Magnetism 2 May 31st 2014 08:32 PM iamET Electricity and Magnetism 1 Oct 22nd 2010 03:37 AM missyc8 Electricity and Magnetism 3 Sep 30th 2009 09:16 AM Mr Rayon Advanced Electricity and Magnetism 1 Mar 29th 2009 07:34 AM jonbrutal Advanced Mechanics 1 Feb 16th 2009 05:57 AM