physics help need help

Question

a.Find the electric field at a point midway between two charges of +43.9 ✕ 10-9 C and +68.2 ✕ 10-9 C separated by a distance of 41.4 cm.


N/C in a direction towards
the +43.9 ✕ 10-9 C charge

Answer 1

Both charges are positive, so at the midpoint, the field points away from the the larger charge, which is towards the 43.9 x 10^-9 C charge.  Calculate the magnitude of the field due to each charge separately, take the difference (since the fields point in opposite directions), and that will be the magnitude of the net field, pointing toward the lower charge.

 

E₁ = kq₁/r² = (9 x 10⁹)(43.9 x 10^-9)/(0.414/2)² N/C = ? N/C

 

E₂ = kq₂/r² = (9 x 10⁹)(68.2 x 10^-9)/(0.414/2)² N/C = ? N/C

 

E_net = E₂ - E₁

 

Now just evaluate the expressions and you are done.