Coulomb’s law: formula, definition, demonstration and solved exercises on the physical force exerted by an electric charge on an electric field.
COULOMB FORCE: DEFINITION AND PROOF
The law of universal gravitation states that: “two bodies, having a certain mass, interact by attracting each other with a force that acts along the line joining the centers of the bodies with an intensity directly proportional to their masses and inversely proportional to the square of their distance” .
Similarly for electric charges we have that “two charges attract or repel each other with a force that acts along the line joining the centers of the two bodies, with an intensity directly proportional to the charges and inversely proportional to the square of their distance” . This is the statement of Coulomb’s law.
COULOMB’S LAW DEFINITION AND FORMULA
The law of universal gravitation is very similar in its statement to what has just been written, but they are substantially very different.
First of all, the law of universal gravitation also applies to moving bodies, whereas Coulomb’s law only applies to stationary charges; the mass must obviously always be positive, whereas the charges can also be negative; furthermore, Coulomb’s force is much greater than the gravitational force that the two charges have.
The formulation of Coulomb’s law is in the force expression written below:
Where q 1 and q 2 are the charges, measured in coulombs [c]; d is their distance [m]; k is the Coulomb constant or constant of proportionality of the electrostatic force defined as
Where ε 0 is the dielectric constant in vacuum, which is 8.85?10 -12 C 2 /Nm 2 .
COULOMB’S LAW: EXERCISE SOLVED
In the statement of Coulomb’s law we are talking about two charges (point and stationary) that attract or repel each other, in particular there is an attractive force between charges of opposite sign and a repulsive force between charges of the same sign.
Let’s look at an example. Calculate the force acting on two point charges of 2.0?10 -6 C and 1.0?10 -6 C at a distance of 10 cm.
Just apply the simple formula seen before, remembering that the Coulomb constant is 8.99?10 9 Nm 2 /C 2 .
INVERSE FORMULA OF COULOMB’S LAW
The request can sometimes be a little different, for example, finding the distance knowing the charges and the force; in this case it is enough to perform the inverse formula of Coulomb’s law .
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