Coulomb's law

F=k\dfrac{q_1 q_2}{r^2}

Result unit: N (newton)

What it describes

The force between two point charges — proportional to the product of the charges and inversely proportional to the square of the distance.

F

force of interaction

[N]

k

electrostatic constant (

\approx 8.99\cdot10^{9}

)

[N·m²/C²]

q_1, q_2

charges

[C]

r

distance between the charges

[m]

Like charges repel, unlike charges attract. The force decreases with the square of the distance — analogous to gravity, but enormously stronger.

Interaction of point charges. The constant

k\approx 9\cdot10^{9}

N·m²/C².

Two charges of 1 µC each are 0.1 m apart. Calculate the force of interaction.

Substitution

q_1=q_2=10^{-6}

r=0.1

k=9\cdot10^{9}

Result

F=9\cdot10^{9}\cdot\dfrac{10^{-12}}{0.01}=0.9

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