Question

A point charge q1 = 1.0 µC is at the origin and a point charge q2 = 6.0 µC is on the x axis at x = 1 m.

(a) Find the electric force on charge q2.
F12 = ? mN
(b) Find the electric force on q1.
F21 = ? mN
(c) What would your answers for Parts (a) and (b) differ if q2 were -6.0 µC?

Answer 1

To solve this problem we will apply the concepts related to the Electrostatic Force given by Coulomb's law. This force can be mathematically described as

`F = (kq_1q_2)/(d^2)`

Here

k = Coulomb's Constant

`q_(1,2) =` Charge of each object

d = Distance

Our values are given as,

`q_1 = 1 \mu C`

`q_2 = 6 \mu C`

d = 1 m

`k =  9*10^9 Nm^2/C^2`

a) The electric force on charge
`q_2` is

`F_(12) = ( (9*10^9 Nm^2/C^2)(1*10^(-6) C)(6*10^(-6) C))/((1 m)^2)`

`F_(12) = 54 mN`

Force is positive i.e. repulsive

b) As the force exerted on
`q_2` will be equal to that act on
`q_1`,

`F_(21) = F_(12)`

`F_(21) = 54 mN`

Force is positive i.e. repulsive

c) If
`q_2 = -6 \mu C`, a negative sign will be introduced into the expression above i.e.

`F_(12) = ((9*10^9 Nm^2/C^2)(1*10^(-6) C)(-6*10^(-6) C))/((1 m)^(2))`

`F_(12) = F_(21) = -54 mN`

Force is negative i.e. attractive