# Determine the current strength in the section of the circuit consisting of

**Determine the current strength in the section of the circuit consisting of a constantan wire 20 m long, with a cross section of 1.2 mm2, if the voltage at the ends of this section is 40 V. r = 0.48 Ohm • mm2 / m**

l = 20 m.

S = 1.2mm ^ 2.

ρ = 0.48 Ohm * mm ^ 2 / m.

U = 40 V.

I -?

According to Ohm’s law for a section of a circuit, the current I is directly proportional to the voltage U and inversely proportional to the resistance of the conductor R: I = U / R.

The resistance of a homogeneous cylindrical conductor R is expressed by the formula: R = ρ * l / S, where ρ is the resistivity of the material from which the conductor is made, l is the length of the conductor, S is the cross-sectional area of the wire.

The formula for determining the current strength I will take the form: I = U * S / ρ * l.

I = 40 V * 1.2 mm ^ 2 / 0.48 Ohm * mm ^ 2 / m * 20 m = 5 A.

Answer: the current in the conductor is I = 5 A.