What electric potential would be measured at a distance of 12cm from a charge of 3.5 x 10-5 c? what would be the potential if the distance were increased to 30 cm?
how much work must be done to carry a 3.0 x 10-5 c charge from 12 cm to 30 cm?

1.

The electric potential produced by a single point charge is

where

k is the Coulomb's constant

q is the charge

r is the distance from the charge

In this problem,

so the electric potential is

2.  

Applying the same formula used before

The electric potential produced by a single point charge is

where in this case we have

the electric potential is

3. 644 J

The work done to carry a charge q through a potential difference of is given by

In this problem, we have

is the charge

is the potential difference

Therefore, the work done is

hypothesising or postulating