# A circuit was assembled from a current source, a lamp and a thin iron wire connected in series.

**A circuit was assembled from a current source, a lamp and a thin iron wire connected in series. The lamp will glow brighter if 1) replace the wire with a thinner 2) increase the length of the wire 3) replace the iron wire with copper 4) swap the wire and the lamp**

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 R of the conductor: I = U / R.

In order for the light to burn brighter, it is necessary for the current to increase. From Ohm’s law, it is necessary to increase the resistance of the circuit 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 wire is made, L is the length of the wire, S is the cross-sectional area.

I = U * S / ρ * L.

To increase the current strength, you can: increase the cross-sectional area of the wire S, reduce the length of the wire L, put a wire with a lower specific resistance ρ.

ρzh = 0.1 Ohm * mm2 / m.

ρm = 0.017 Ohm * mm2 / m.

Answer: there are no correct answers.