Step-by-step explanation:
The electric field is defined as the ratio of electric field per unit test charge. Mathematically, it can be written as :

F is the electrostatic force i.e.

...........(1)
Where
r is the distance from the one charge to test charge
Q is the source charge
k is electrostatic constant, k = 9 × 10⁹ N-m²/C²
Hence, the electric field strength at a distance r is given by equation (1)