# Help needed on a couple questions

1. Sep 20, 2006

### swami85

help needed on a couple questions - electric fields

anyone able to lend a hand?

1. How many excess electrons must be added to an isolated spherical conductor of diameer 30.0 cm to produce an electric field of 1155 N/C just outside the surface?

permittivity of free space and charge on an electron are given

2. A very long uniform line of charge has charge per unit length 4.62 \mu C/m and lies along the x-axis. A second long uniform line of charge has charge per unit length -2.46 \mu C/m and is parallel to the x-axis at y_1 = 0.414 m.

What is the magnitude of the net electric field at point y_2 = 0.188 m on the y-axis?

for this one i think it's along the lines of E = lamda/ 2 pi ep_0 r, but i'm not sure of which values are to be used

and...

3. The electric field at a distance 0.485 m from a very long uniform line of charge is 880 N/C.
How much charge is contained in a section of the line of length 2.00 cm?

i don't want the answer but help on how to solve the questions

Last edited: Sep 20, 2006
2. Sep 21, 2006

### Staff: Mentor

What equations relate charge distributions to electric field?