Electrical Voltage
The voltage corresponds to a potential difference between two points
a different circuit. The unity of the (pd) is the VOLT (V), symbolized by the letter U.
To measure this , you should use a voltmeter v. This one is always parallel branch
on the circuit.
It is also called electromotive force (emf) and thanks to its action that the electrical current may exist.
The greater the voltage, the greater the flow of electrical current (that is, the quantity of charge carriers that pass a fixed point per unit of time) through a conducting or semiconducting medium for a given resistance to the flow. Voltage is symbolized by an uppercase italic letter V or E. The standard unit is the volt, symbolized by a non-italic uppercase letter V. One volt will drive one coulomb (6.24 x 1018) charge carriers, such as electrons, through a resistance of one ohm in one second.
A voltage produces an electrostatic field, even if no charge carriers move (that is, no currentflows). As the voltage increases between two points separated by a specific distance, the electrostatic field becomes more intense. As the separation increases between two points having a given voltage with respect to each other, the electrostatic flux density diminishes in the region between them.
1) voltage Notion:
a- Terminal voltage of a battery:
The negative terminal of a battery has an excess of electrons and these electrons are in default at the positive terminal. The size represents the charge concentration is called "electrical potential".
Between the two terminals P and N of the stack there exists a "potential difference" (noted VP-VN) or "voltage" (rated UPN)
It is because of this potential difference that the battery is capable of moving free electrons, it is called "electromotive force" of the stack.
Note: The elevation of a place can be defined only in relation to an altitude marker (sea level, level of an aerodrome ...)
Similarly, the potential at a point can be defined only by its difference with a reference potential ("ground" of the circuit, the negative potential ...)
b-Tension between two points of a circuit:
For a given closed loop, over the electromotive force (emf) of the cell, the greater the current flowing in the circuit is intense.
The electron concentration varies throughout the circuit. This is the negative that it is the strongest and the positive it is the lowest.
The potential V is the maximum and minimum positive to the negative terminal.
Between points A and B of a circuit can be defined as a potential difference (VA-VB) or voltage (UAB).
2) Measurement of the voltage:
a- Unit of voltage:
The unit of voltage is the volt (in tribute to Alessandro Volta)
The symbol of the volt is V.
Measuring a voltage:
For measuring a voltage we use a voltmeter.
The voltmeter symbol is:
b-Use of a voltmeter:
To measure the voltage between two points A and B of a circuit, connecting a voltmeter in parallel between these two points.
The terminal marked V must be connected to point A and the terminal marked COM to point B. It then measures the voltage UAB
If we ignore the magnitude of the voltage to be measured, it is prudent to place the voltmeter to its highest caliber when connecting.
It must then reduce this caliber, if necessary, for better display: The right size is the smallest size immediately above measure.
3) Voltage in circuits:
a- Terminal voltage of a single dipole:
If the voltage across an isolated dipole is not zero, the dipole is a generator.
Note: A voltage can exist in the absence of any electric current.
b-Voltage between the terminals of a dipole, traversed by a current:
If a dipole is traversed by a current, a voltage between its terminals exist.
Note: A current can not flow in the absence of tension.
.Case of a connecting wire:
The voltage between the two ends of a good bonding wire is negligible.
Note: The wire should not be too long nor too short. Its electrical resistance should be negligible compared to the resistance of the rest of the circuit.
.Case of a switch:
The voltage across a closed switch is negligible as the voltage across a wire.
The voltage across an open switch is equal to the voltage at the generator terminals (single circuit) or to the voltage across the branch in which it is placed.
Consequence: When a receiver is connected to a generator by good wire connection, the voltage at the receiver terminals is equal to the voltage of the generator since there is no "voltage drop" in connection wires.
c-Additivity law tensions in a series circuit:
The voltage across a set of dipoles in series is equal to the sum of the voltages across each of them.
In the example below c:
P and A are the same potential
B and C are at the same potential
D and N are the same potential
d-Law of equal tensions in a bypass circuit:
Two dipoles connected in shunt to the terminals of a generator are subject to the same voltage of that generator.
In the example below :
P, E, A and C are at the same potential
N, F, B and D are at the same potential
UPN = UEF = UAB = UCD
Generalization:
We can take any three points A, B, C of a circuit in which the potentials are respectively VA, VB, VC.
UAB + UBC = (VA - VB) + (VB -VC)
UAB + UBC = VA - VB + VB - VC = VA - VC
UAB + UBC = UAC
4) Short circuit:
A short circuit occurs when two wires having different potentials come into contact.
The dipole whose terminals are connected by a conductor is shorted.
A short-circuited dipole ceases to operate because the voltage at its terminals becomes negligible and the current flowing through it is negligible.
The intensity increases in the circuit because the electrical resistance of the short circuit is much lower than that of the short-circuited dipole.
When a generator is short-circuited, the output current can be very important because it is constrained by the internal resistance of the generator and the resistance of the wire (very low). This current can destroy the generator or strongly warm the wire until a fire.
Note: A battery has a lower internal resistance than that of a battery. A short circuit destroys in a short time, whereas a battery can withstand a short circuit for a few seconds.
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