electrokinetic

Electrokinetics studies electric current and its effects. Electric current is an orderly movement of electrical charges.

Simple electrical circuit

Simple circuit with a source, a light bulb and an open switch The bulb does not light up.	Simple circuit with a source, a light bulb and a closed switch The light bulb lights up.

 

Simple, open circuit with a source and a consumer No current is flowing.	Simple, closed circuit Current flows.

 

Electrical dimensions

It circulates through the electrical circuit electric charge q:

$${⟨q⟩}_{\mathit{SI}}=1C(\mathit{Coulomb})$$

Current intensity I shows how much electric charge passes per unit time through any section of the simple circuit:

$$I=\frac{\mathrm{\Delta }q}{\mathrm{\Delta }t},{⟨I⟩}_{\mathit{SI}}=1C/s=1A(\mathit{Amper})$$

The conventional direction of current through the circuit has been established to be the direction in which positive charges would flow: they are repelled by the + terminal of the voltage source and attracted by the – terminal of the source.

 

The determining factor of the flow of electric charge is electrical voltage. Without voltage, current does not flow. Voltage UAB between 2 points A, B along the circuit represents the mechanical work that the source must perform to force the passage of 1C of electric charge on the circuit portion AB:

$$U_{\mathit{AB}}=\frac{L_{\mathit{AB}}}{\mathrm{\Delta }q},{⟨U⟩}_{\mathit{SI}}=1J/C=1V(\mathit{Volt})$$

 

Electric potential represents the energy of the unit of electric charge relative to a reference point of the circuit.

Optionally, the - terminal of the voltage source can be connected to the Earth (earthing) or to the ground, at point G (ground), taken as a reference point. The electric charges reached at that point have no more energy and their electric potential at that point is 0:VG=0.

On the other hand, at the point S (at the + terminal) the electric charges have the maximum possible energy, and the electric potential is also maximum at the point S.

Current and voltage can be measured directly with measuring instruments: ammeter and voltmeter.

Electrical resistance shows how much a portion of the circuit (or a circuit element) resists the flow of current.

$$R_{\mathit{AB}}=\frac{U_{\mathit{AB}}}{I},{⟨R⟩}_{\mathit{SI}}=1V/1A=1\mathrm{\Omega }(\mathit{Ohm})$$

Ohm's law

This law is stated in two versions:

1. Ohm's law for a portion of a circuit:

The intensity of the current is directly proportional to the voltage:

$$I=\frac{U_{\mathit{AB}}}{R_{\mathit{AB}}},U_{\mathit{AB}}=I\cdot R_{\mathit{AB}}$$

UAB is the voltage drop on the circuit portion AB, and RAB is the electrical resistance of that portion.

2. Ohm's law for the entire circuit:

The electromotive voltage of the source is equal to the sum of the voltage drops throughout the circuit, including the voltage drop on the internal resistance of the source:

$$E=U+u,U=I\cdot R,u=I\cdot r$$

U is the voltage drop across all external elements of the circuit, and u is the voltage drop across the internal resistance.

Simple circuit with several consumers

 

Electric potentials in an electric circuit

 

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