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 :
![E=(F)/(q)](https://img.qammunity.org/2020/formulas/physics/middle-school/rd627zvztvryx8r63bpbbe8cpfd3t3gkl0.png)
F is the electrostatic force i.e.
![F=k(Qq)/(r^2)](https://img.qammunity.org/2020/formulas/physics/middle-school/qi5v078vi2i16xlmruxo7rlhcel10evxqp.png)
...........(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)