For a person who is familiar with electrical equipment at the simple user level (knows where and how to turn it on / off), many of the terms used by electricians seem like some kind of nonsense. For example, what does “voltage drop” or “circuit assembly” cost? Where and what is falling? Who disassembled the circuit for details? In fact, the physical meaning of the processes, which is hidden behind most of these words, is quite understandable even with school knowledge of physics.
In order to explain what a voltage drop is, it is necessary to recall what voltages are in an electric circuit in general (meaning global classification). There are only two types of them. The first is the voltage of the power source, which is connected to the circuit in question. It may also be called attached to the entire chain. And the second view is precisely the voltage drop. It can be considered both in relation to the entire contour, and any single element.
In practice, this is as follows. For example, if you take a conventional incandescent lamp, screw it into a cartridge, and connect the wires from it to a home power outlet, then the voltage applied to the circuit (power source - conductors - load) will be 220 volts. But if we use a voltmeter to measure its value on the lamp, it will become obvious that it is slightly less than 220. This happened because a voltage drop occurred on the electrical resistance that the lamp has.
Perhaps there is no person who would not hear about Ohm's law. In general, its wording looks like this:
I = U / R,
where R is the active resistance of the circuit or its element, measured in Ohms; U is the electrical voltage in Volts; and finally, I is the current in Amperes. As you can see, all three values are directly related. Therefore, knowing any two, you can quite easily calculate the third. Of course, in each specific case it will be necessary to take into account the type of current (alternating or constant) and some other clarifying characteristics, but the basis is the above formula.
Electrical energy is, in fact, the movement along the conductor of negatively charged particles (electrons). In our example, the lamp spiral has a high resistance, that is, it slows down the moving electrons. Due to this, a visible glow occurs, but the total energy of the particle stream decreases. As can be seen from the formula, with a decrease in current, the voltage also decreases. That is why the results of measurements at the outlet and on the lamp differ. This difference is a voltage drop. This value is always taken into account to prevent too large a decrease in the elements at the end of the circuit.
The voltage drop across the resistor depends on its internal resistance and the strength of the current flowing through it. Also indirectly influenced by temperature and current characteristics. If an ammeter is included in the circuit under consideration, then the drop can be determined by multiplying the current value by the lamp resistance.
But it is far from always possible to simply calculate the voltage drop using the simplest formula and a measuring device. In the case of parallel-connected resistances, finding the value is complicated. On alternating current, the reactive component must be additionally taken into account.
Consider an example with two resistors R1 and R2 connected in parallel. The resistance of wire R3 and power source R0 is known. Also given is the EMF value - E.
We bring parallel branches to one number. For this situation, the formula applies:
R = (R1 * R2) / (R1 + R2)
We determine the resistance of the entire circuit through the sum R4 = R + R3.
We calculate the current:
I = E / (R4 + r)
It remains to find out the value of the voltage drop on the selected element:
U = I * R5
Here the factor "R5" can be any R - from 1 to 4, depending on which particular circuit element needs to be calculated.