Coulomb's Law (Electric Force) Video Lessons

Concept

# Problem: Two charged particles, with charges q1 = q and q2 = 4q, are located at a distance d = 2.00cm apart on the x-axis. A third charged particle, with charge q3 = q, is placed on the x-axis such that the magnitude of the force that charge 1 exerts on charge 3 is equal to the force that charge 2 exerts on charge 3. Find the position of charge 3 when q = 2.00 nC.  Assuming charge 1 is located at the origin of the x-axis and the positive x-axis points to the right, find the two possible values, x3,r and x3,l for the position of charge 3.

###### FREE Expert Solution

Coulomb's law for point charges::

$\overline{){\mathbf{F}}{\mathbf{=}}\frac{\mathbf{k}{\mathbf{q}}_{\mathbf{1}}{\mathbf{q}}_{\mathbf{2}}}{{\mathbf{r}}^{\mathbf{2}}}}$

$\overline{){\mathbf{x}}{\mathbf{=}}\frac{\mathbf{-}\mathbf{b}\mathbf{±}\sqrt{{\mathbf{b}}^{\mathbf{2}}\mathbf{-}\mathbf{4}\mathbf{a}\mathbf{c}}}{\mathbf{2}\mathbf{a}}}$

Expansion formular:

$\overline{){{\mathbf{\left(}}{\mathbf{a}}{\mathbf{-}}{\mathbf{b}}{\mathbf{\right)}}}^{{\mathbf{2}}}{\mathbf{=}}{{\mathbf{a}}}^{2}{\mathbf{-}}{\mathbf{2}}{\mathbf{a}}{\mathbf{b}}{\mathbf{+}}{{\mathbf{b}}}^{{\mathbf{2}}}}$

d = 2.00 cm(1m/100cm) = 0.02 m

Assume the third charge is located between the two charges such that:

r13 = (d - x) m

r23 = x m

q1 = q = 2.00 nC(10-9C/1nC) = 2.00 × 10-9 C

q2 = 4q = 8.00 nC(10-9C/1nC) = 8.00 × 10-9 C

q3 = q = 2.00 nC(10-9C/1nC) = 2.00 × 10-9 C

We are told that F13 = F23:

$\begin{array}{rcl}{\mathbf{F}}_{\mathbf{13}}& \mathbf{=}& {\mathbf{F}}_{\mathbf{23}}\\ \frac{\overline{)\mathbf{k}}{\mathbf{q}}_{\mathbf{1}}\overline{){\mathbf{q}}_{\mathbf{3}}}}{{\mathbf{\left(}{\mathbf{r}}_{\mathbf{13}}\mathbf{\right)}}^{\mathbf{2}}}& \mathbf{=}& \frac{\overline{)\mathbf{k}}{\mathbf{q}}_{\mathbf{2}}\overline{){\mathbf{q}}_{\mathbf{3}}}}{{\mathbf{\left(}{\mathbf{r}}_{\mathbf{23}}\mathbf{\right)}}^{\mathbf{2}}}\\ \frac{\mathbf{2}\mathbf{.}\mathbf{00}\mathbf{×}\overline{){\mathbf{10}}^{\mathbf{-}\mathbf{9}}}}{{\mathbf{\left(}\mathbf{0}\mathbf{.}\mathbf{02}\mathbf{-}\mathbf{x}\mathbf{\right)}}^{\mathbf{2}}}& \mathbf{=}& \frac{\mathbf{8}\mathbf{.}\mathbf{00}\mathbf{×}\overline{){\mathbf{10}}^{\mathbf{-}\mathbf{9}}}}{{\mathbf{x}}^{\mathbf{2}}}\\ \mathbf{2}{\mathbf{x}}^{\mathbf{2}}& \mathbf{=}& \mathbf{8}\mathbf{\left(}{\mathbf{x}}^{\mathbf{2}}\mathbf{-}\mathbf{0}\mathbf{.}\mathbf{04}\mathbf{x}\mathbf{+}\mathbf{0}\mathbf{.}\mathbf{0004}\mathbf{\right)}\\ \mathbf{0}& \mathbf{=}& \mathbf{8}{\mathbf{x}}^{\mathbf{2}}\mathbf{-}\mathbf{2}{\mathbf{x}}^{\mathbf{2}}\mathbf{-}\mathbf{0}\mathbf{.}\mathbf{32}\mathbf{x}\mathbf{+}\mathbf{0}\mathbf{.}\mathbf{0032}\\ & \mathbf{=}& \mathbf{6}{\mathbf{x}}^{\mathbf{2}}\mathbf{-}\mathbf{0}\mathbf{.}\mathbf{32}\mathbf{x}\mathbf{+}\mathbf{0}\mathbf{.}\mathbf{0032}\end{array}$

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###### Problem Details
Two charged particles, with charges q1 = q and q2 = 4q, are located at a distance d = 2.00cm apart on the x-axis. A third charged particle, with charge q3 = q, is placed on the x-axis such that the magnitude of the force that charge 1 exerts on charge 3 is equal to the force that charge 2 exerts on charge 3.

Find the position of charge 3 when q = 2.00 nC.  Assuming charge 1 is located at the origin of the x-axis and the positive x-axis points to the right, find the two possible values, x3,r and x3,l for the position of charge 3.