Task Sets: Coulomb's Law - OpenStax Physics (High School)

Fluency Practice

Use $k = 9 \times 10^9$ N·m²/C². Show your work and state the direction of each force.

Two protons are separated by a distance $r$ . Which of the following correctly describes the electric force between them?

Attractive, with magnitude $F = \frac{k e^2}{r^2}$

Repulsive, with magnitude $F = \frac{k e^2}{r^2}$

Attractive, with magnitude $F = \frac{k e}{r^2}$

Zero — protons are too small to exert detectable forces.

Calculate the magnitude of the electric force between two charges: $q_1 = +3 \times 10^{-6}$ C and $q_2 = +5 \times 10^{-6}$ C, separated by $r = 0.30$ m. Express your answer in newtons to two significant figures.

Calculate the magnitude of the electric force between $q_1 = +2 \times 10^{-6}$ C and $q_2 = -4 \times 10^{-6}$ C separated by $r = 0.20$ m. Express your answer in newtons to two significant figures.

The electric force between two charges separated by distance $r$ is $F$ . If the distance is doubled to $2r$ (charges unchanged), what is the new force?

$\frac{F}{2}$ — distance doubled, force halved

$\frac{F}{4}$ — distance doubled, force reduced by factor of 4

$2F$ — force doubles when distance doubles

$4F$ — force quadruples when distance doubles

A number line showing three charges: A (+4 μC) at 0 m, B (−2 μC) at 0.30 m, and C (+3 μC) at 0.50 m

Three charges are on a line. Charge A ( $+4 \mu$ C) is at position 0, charge B ( $-2 \mu$ C) is at 0.30 m, and charge C ( $+3 \mu$ C) is at 0.50 m. Find the net force on charge B.

Taking rightward as positive, what is the net force on B in newtons? (Positive = right, negative = left.) Express your answer to two significant figures.

In the same setup (A at 0, B at 0.30 m, C at 0.50 m), what is the net force on charge C? (Positive = right, negative = left.) Express your answer to two significant figures.

Exercises: Coulomb's Law

Warm-Up: Prerequisite Review

Fluency Practice