How to define an electric charge


Schoolchildren, who studied physics in high school, surely know the simplest instrument – the electrometer. It consists of a metal bar with a round horizontally arranged protrusion. On this protrusion there is an arrow that can rotate freely. What happens if the metal rod of an electrometer is touched by a charged body? Part of the charge kind of flows over to the rod and arrow. But since these charges are eponymous, they will push each other away. And the arrow will deviate from the original position by some angle. With the help of a graduated scale, it is measured and the amount of charge is calculated. It is easy to understand that the larger the charge, the greater the angle of deflection of the electrometer arrow will be, and vice versa. Of course, with such a primitive instrument, only an approximate determination of the magnitude of the charge can be made. If high accuracy is needed, sensitive electronic electrometers are applied.


You can use Coulomb’s law: F = kq1q2/r^2, where F is the force of interaction between two charged bodies, q1 and q2 are the values of their charges, r โ€” the distance between the centers of these bodies, and k is the proportionality coefficient. In other words, if you have a body whose charge q1 is known to you, then by raising the second body whose charge q2 needs to be determined by distance r and the force of interaction F using a sensitive instrument dynamometer, you easily calculate the desired charge q2 using the formula: q2 = Fr^2/ (kq1).


It is

also possible to clean out the amount of charge by measuring the current in the circuit. The fact is that the total value of the charge flowing through the cross section of a conductor is calculated by the formula: Q = IT, where I is the current in amperes and T is the time in seconds. For this experience, you will need a stopwatch and an ammeter โ€” a device for determining the current. Assemble the electrical circuit where the ammeter is turned on, turn on the current, write down the ammeter reading. Unlock the circuit while turning off the stopwatch at the same time. Write down how long the current was in the circuit. And by the above formula, count the total electric charge.

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