Answer:
r = 0.338 meters
Step-by-step explanation:
Q = Source charge
q = Test charge
5μC= 5*10^-6 C
Start with the electric field equation:
![E = (F)/(q)](https://img.qammunity.org/2023/formulas/physics/high-school/v8bfpsbpma0b05me7v5sagcwzyji88d5ix.png)
and Coulombs law
![F=(k|Qq|)/(r^2)](https://img.qammunity.org/2023/formulas/physics/high-school/edm56pljt7avo4859q4mqn4al8zzy7qqko.png)
Combining these functions we get:
![E=(k|Q|)/(r^2)](https://img.qammunity.org/2023/formulas/physics/high-school/2g9pyhvapuwozclbreabcvn1qwxjxf0b70.png)
As you can see the test charge cancels so we do not need the value of it.
Plug in your numbers:
![3.93*10^5=((8.99*10^9)(5*10^-^6))/(r^2)](https://img.qammunity.org/2023/formulas/physics/high-school/fp3ld92fnhp4k63hn1kqd2c87ciu97uvof.png)
solve for r
![r=\sqrt{((8.99*10^9)(5*10^-^6))/((3.93*10^5)) }](https://img.qammunity.org/2023/formulas/physics/high-school/r1841as3i4wxjbli4i0tzj72uzq6pe40ed.png)
![r= 0.338 meters](https://img.qammunity.org/2023/formulas/physics/high-school/2gohy8j3q7g82bugrd3v49fwb18vw0uyl9.png)