Physics

Problem

Which one of the following expressions represents the electrostatic force on charge

q_2

due to charge

q_1

separated by a distance

r

in vacuum? a)

k\dfrac{q_1q_2}{r}\,\hat{\mathbf r}_{12}

k\dfrac{q_1q_2}{r^{2}}\,\hat{\mathbf r}_{21}

k\dfrac{q_1q_2}{r^{2}}\,\hat{\mathbf r}_{12}

k\dfrac{|q_1q_2|}{r^{2}}\,\hat{\mathbf r}_{12}