Given:
The charge q1 = 8.42 nC
The charge q2 = -3.75 nC
The distance between the charges is d = 2.73 cm
To find the electric field strength at the midpoint between the two charges.
Explanation:
The distance between the charges and the midpoint is d' =d/2
The electric field strength can be calculated by the formula

The electric field strength at the midpoint due to the charge q1 will be

The electric field strength at the midpoint due to the charge q2 will be

The electric field strength at the midpoint between the charges will be

The electric field strength at the midpoint between the two charges is 5.87 x 10^(5) m.
Answer:

Explanation:
The electric field is defined as the electric force per unit of charge, this is:
.
The electric force can be obtained through Coulomb's law, which states that the electric force between to electrically charged particles is inversely proportional to the square of the distance between them and directly proportional to the product of their charges. The electric force can be expressed as
.
By substitution we get that

Now, letting
be the electric field at point A, letting
be the electric field at point B, and letting R be the distance from the charge to A:
.
The ration of the electric fields is

This means that at half the distance, the electric field is four times stronger.