Electric Fields and charges of equal magnitude

[mli273]

1. Two point charges of equal magnitude are 8.4 cm apart. At the midpoint of the line connecting them, their combined electric field has a magnitude of 45 N/C.

Find the magnitude of the charges.



2. E=k(q)/r^2



3. I've tried 45= 8.99x10^9(q)/(.084)^2 and got q to equal 35 pC, but that isn't correct :(

 

[alphysicist]

Hi mli273,

1. Two point charges of equal magnitude are 8.4 cm apart. At the midpoint of the line connecting them, their combined electric field has a magnitude of 45 N/C.

Find the magnitude of the charges.



2. E=k(q)/r^2



3. I've tried 45= 8.99x10^9(q)/(.084)^2 and got q to equal 35 pC, but that isn't correct :(

The quantity 8.99x10^9(q)/(.084)^2 gives the magnitude of the electric field from one charge q at a distance 8.4 cm away from that charge. Do you see why that is wrong for this problem, and what to do now?