Among other indicators characterizing the electrical circuit, the conductor, it is worth highlighting electrical resistance. It determines the ability of the material atoms to impede the directional passage of electrons. Assistance in determining this value can provide both a specialized device - an ohmmeter and mathematical calculations on the basis of knowledge of the relationship between the values \u200b\u200band physical properties of the material. The measurement of the indicator is made in Omah (OM), the symbol R.
OMA's law is a mathematical approach when determining resistance
The ratio set by George Omom determines the relationship between the voltage, current force, resistance based on the mathematical relationship of concepts. The validity of the linear relationship is R \u003d U / I (voltage ratio to current) - notes not in all cases.
Unit of measurement [R] \u003d b / a \u003d Ohm. 1 Ohm is the resistance of the material by which current in 1 amp at a voltage of 1 volt.
Empirical formula for calculating resistance
Objective material on the conductivity of the material is followed from its physical characteristics, defining both its own properties and reactions to external influences. Based on this, the conductivity depends on:
- Size.
- Geometry.
- Temperature.
The atoms of the conductive material are faced with directional electrons, preventing further advancement. At high concentration of the latter, atoms are not able to resist them and conductivity is high. Large resistance values \u200b\u200bare characteristic of dielectrics that differ almost zero conductivity.
One of the defining characteristics of each conductor is its specific resistance - ρ. It determines the dependence of the resistance from the material of the conductor and exposure to the outside. This is fixed (within the same material) the value that represents the data of the conductor of the following sizes - the length is 1 m (ℓ), the cross-sectional area of \u200b\u200b1 sq.m. Therefore, the relationship between these values \u200b\u200bis expressed by the relation: R \u003d ρ * ℓ / S:
- The conductivity of the material falls as its length increases.
- An increase in the cross section of the conductor entails a decrease in its resistance. Such a pattern is due to a decrease in the density of electrons, and, consequently, the contact of the particles of the material with them becomes more rare.
- The growth temperature of the material stimulates the growth of resistance, while the drop in temperature entails its decline.
The calculation of the cross-section area is advisable according to the formula S \u003d πd 2/ 4. Roulette will help in determining the length.
Power relationship (P)
Based on the formula of the OM, U \u003d I * R and P \u003d I * U. Consequently, P \u003d I 2* R and P \u003d U 2/ R.
Knowing the amount of current and power, resistance can be defined as: R \u003d P / I 2.
Knowing the amount of voltage and power, resistance is easy to calculate according to the formula: R \u003d U 2/ P. 
The resistance of the material and the magnitude of other concomitant characteristics can be obtained using special measuring instruments or on the basis of established mathematical patterns.
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The resistance of the conductors is measured, and not current. Current has no resistance.
Thanks a lot! Long searched!