Getting Started to determine the numerical expression of the current voltage, you should decide on the terminology. The voltage on the plot of the electrical circuit characterizes the work performed on the transfer of a positive unit charge (or energy that is released when moving the charge) from one point to another. The initial and endpoints are characterized by the potential, as a result of which the voltage is still referred to as the difference in potentials or electromotive force. The value is denoted by the letter U, its measurement is carried out in volts (b). Determine the tension, having a voltmeter in the hands, will not be difficult. However, if this device is not, the knowledge of the relationship between other characteristics of the electrical circuit and the voltage will help to establish the desired value.
Learn voltage through the Ohm law
Having numeric currents of current (I) and resistance (R), find an unknown component, voltage will help the law of Oma. Its formula i \u003d u / r. It reflects the direct proportional relationship of the voltage-strength of the current, and inversely proportional ratio the resistance voltage on a specific section of the chain. The prescribed pattern is valid for sections of both constant and alternating current. The relationship U \u003d I * R is not a fundamental law. It only shows an empirical ratio between values \u200b\u200bunder certain conditions.
The law does not always work in such cases:
- In some heterogeneous devices (diodes, transistors).
- In cases of high frequencies.
- At low temperatures (for superconductors).
- Upon explicit heating of the element in the process of passing on it (as in the case of incandescent lamp).
- In electronic lamps containing vacuum or gas (fluorescent lamps).
- Touching the conductor or dielectric high voltage, resulting in the appearance of a breakdown.
Physical decoding of the Ohm Law to find out the voltage
"Classic" presentation of the law does not take into account some properties of a conductive material, so it is correct only from a mathematical point of view. Considering the physical characteristics of the conductor allows another interpretation of the law: u \u003d I * ℓ * ρ / S, where
I - current strength
ρ - the resistivity of the conductor,
ℓ - Length,
S is a cross-section of the material (area). 
Voltage definition using power value
Georg Simon OM set the following relationship between resistance and power: R \u003d P / I 2 and r \u003d u 2/ P, therefore p \u003d i * u. It follows from this that u \u003d p / i.
Relationship with work (A)
Based on the determination of the voltage, it is possible to determine its numerical expression, knowing the amount of operation. The connection of these characteristics is expressed as a formula U \u003d A / Q. It defines the ratio of current operation to the charge passed through this section of the chain.
All the characteristics needed to calculate the voltage can be obtained from the instructions for electrical appliances, or using the appropriate measuring instruments.
2
753
