10. The following three point charges are placed on the x axis: +5.0 mC at x=0; +4.0 mC at x= -40 cm; and +6.0 mC at x= +80 cm. Find (a) the electric field magnitude and direction and (b) the electric potential at x= +10 cm.

Question

10.   The following three point charges are placed on the x axis: +5.0 mC at x=0; +4.0 mC at x= -40 cm; and +6.0 mC at x= +80 cm.  Find (a) the electric field magnitude and direction and (b) the electric potential at x= +10 cm.

a)  E = k(5E-6)/.102 +k(4E-6)/.502 - k(6E-6)/.702 = +4.5E6  N/C (in +x direction)

I was just wondering, how did the teacher get .102, .502 and .702 as the radius's.

drwls · Answer

x is 0.70 m from the 6 mC charge, 0.50 m from the 4 mC charge, and 0.10 m from the 5 mC charge

I also do not understand why the number "0.002" was added to those distances (in meters). It appears to be a misprint.