Elctric field problems

[mustang]

Problem 3.
Given: k_e=8.98755*10^9 Nm^2/C^2 and g=9.81m/s^2.
An electron is released above the Earth's surface. A second electron directly below it exerts just enough of an electric force on the first electron to cancel the gravitational force on it.
Find the distance between the two electrons?
Note: What formula would you use?

Problem 18.
Given: k_e=8.98755*10^9Nm^2/C^2.
The dome of a van de Graaff generator receives a charge of .6*10^-4 C. The radius of the dome is 5.7m.
Find the magnitude of the electric field strength inside the dome. In units of N/C.
Note: What formula would you use and what to do first?

Problem 21.
Thunderstorms can have an electric field of up to 3.37*10^5 N/C.
What is the magnitude of the electric force on an electron in such a field?
Note: What would I do first?

[himanshu121]

Use Coulombs law , use the relation between Electric field and Force

[mustang]

For problem 18 then of having to find magnitude of the electric field strength inside the dome how would I find the magnitude of the electric field strength at the surface of the dome and the magitude of the electric field strength at the surface of the dome?

[gnome]

Have you learned Gauss's law?

Is there any charge inside the dome?

[mustang]

No I haven't learned Gauss' law.
There is 0 electric field strength inside the dome,