# Electrical resistance

Electrical resistance is a physical quantity that characterizes a conductor's ability to impede the movement of electric charges. For direct current (DC), the resistance of a conductor is calculated by the formula:

$$R=\rho \cdot \frac{l}{A}$$

where,

l— length of the conductor in meters;
A— cross-sectional area of the conductor in square meters;
q— specific resistance of the material in ohm-meters.

In a direct current circuit without an electromotive force source, the resistance $$R$$ is equal to the ratio of the applied voltage $$U$$ to the current $$I$$ flowing through the circuit:

$$R=\frac{U}{I}$$

where,

U— applied voltage to the electric circuit;
I— current intensity flowing through the circuit.

Unit of resistance in the International System of Units (SI) is the ohm (Ω). The resistance of a part of an electric circuit is 1 ohm when a voltage of one volt (1V) across the ends of the circuit produces a current intensity of one ampere (1A) in that circuit segment.