If the same current passes through a copper wire and an iron wire of equal length and cross-sectional area, which statement is true?
- AThe heat produced is the same in both the copper wire and the iron wire
- BThe heat produced is more in the copper wire than in the iron wire
- CThe heat produced is more in the iron wire than in the copper wire
- DIt cannot be compared without the potential difference
Show answer and explanation
Correct answer: (c) The heat produced is more in the iron wire than in the copper wire
Explanation
By Joule's law, H = I²Rt. The current and time are the same, so the heat depends on the resistance of each wire.
For wires of the same length and cross-section, R = ρL/A, so R depends only on the resistivity ρ:
- copper: about 1.7 × 10⁻⁸ Ω·m;
- iron: about 10 × 10⁻⁸ Ω·m.
Iron has the higher resistance, so more heat is produced in the iron wire. This is also why copper is used for connecting wires: it wastes less energy as heat.