measurments and calculations

resistance

Resistance
Resistance and reactance are terms from physics which are part of the complex field of materials and their effects on electricity. However, in reality, resistance and reactance are easy to understand.

Resistance is the ratio of electrical potential (voltage) to the current in a material. Simply put, a material with high resistance requires a high potential to generate a given amount of current in the material. A material with low resistance requires a low potential to generate the same amount of current.

Perhaps the easiest way to think about this is to say that a material with low resistance conducts well, while a material with high resistance conducts poorly.

Steel, which conducts well, is said to have low resistance. Wood which conducts poorly, is said to have high resistance. Because of its electrolyte (charged ion) content, salt water conducts well and has low resistance, while pure water conducts poorly and is said to have high resistance.

When a material is conducting, it releases energy in the form of heat. Therefore, the resistance of a material is related to the material's ability to dissipate energy. Units of resistance are called ohms.

In the human body, low resistance is associated with large amounts of fat-free mass. High resistance is associated with smaller amounts of fat-free mass.
Why is this the case?
The primary conductor in the human body is ionized water. As the percentage of body weight that is water increases, the conductivity of the body increases. Since body water is contained solely within fat-free mass, the conductivity of the body is proportional to the amount of fat-free mass.

How is resistance measured?
A small current is applied through the body. The potential required to generate the current is measured. The ratio of potential and current along with a process called correlation and integration are used to determine the resistance and reactance respectively.
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