Adding the fields of point charges in code

You will write three small functions about the electric field of point charges. They use $E = kQ/r^2$ and the rule that fields add as vectors.

The idea. The constant is $k = 9.0 \times 10^{9}\ \text{N m}^2/\text{C}^2$. Charges are given in nC and distances in metres. On a line, a field towards $+x$ is positive and a field towards $-x$ is negative. The field of a positive charge points away from it. The field of a negative charge points towards it.

Your tasks.

1. In point_field, return the size of the field of one charge q_nc (in nC) at a distance r (in m), in N/C.
2. In net_field_on_line, charges is a list of (charge in nC, position in m) on the $x$ axis. Return the net field at the position x, in N/C, with the sign described above.
3. In zero_point, two charges of the same sign, q1_nc and q2_nc, are a distance d apart. Return the distance from the first charge to the point between them where the field is zero.