TP 19.34

Given:

 q₁ = +6.20 mC at x = 0 

q₂ = -9.50 mC at x = 10.0 cm

(a) Find: E_tot at  x = - 4.00 cm?

  E₁ = k |q₁| / r₁² = (8.99 x 10⁹ N m² /C²) (6.20 x 10^-6 C)/ (0.040 m )² = 34,836 x 10³ N/C, to the left

 E₂ = k |q₂| / r₂² = (8.99 x 10⁹ N m² /C²) (9.50 x 10^-6 C)/ (0.140 m )² = 4,357 x 10³ N/C, to the right

 E_tot= E₁ + E₂ = -34,836 x 10³ N/C + 4,357 x 10³ N/C = - 30, 478 x 10³ N/C (Note, electric field is directed to the left.)

(b) Find: E_tot at  x =  4.00 cm?

  E₁ = k |q₁| / r₁² = (8.99 x 10⁹ N m² /C²) (6.20 x 10^-6 C)/ (0.040 m )² = 34,836 x 10³ N/C, to the right

 E₂ = k |q₂| / r₂² = (8.99 x 10⁹ N m² /C²) (9.50 x 10^-6 C)/ (0.060 m )² = 23,724 x 10³ N/C, to the right

 E_tot= E₁ + E₂ = 34,836 x 10³ N/C + 23,724 x 10³ N/C = 58,560 x 10³ N/C (Note, electric field is directed to the right.)