Question

The resistivity of hard drawn copper at 20 °C is 1.9 × 10^-6 Ω cm. The resistivity of annealed copper compared to hard drawn copper is
1. lesser
2. slightly larger
3. same
4. much larger

Answer 1

Correct Answer - Option 1 : lesser

• Soft drawn copper (or annealed copper) has a lower breaking strength than hard drawn copper. It has lower resistivity compared to hard drawn copper.
• The resistivities of annealed and hard drawn copper at 20° C respectively are 1.72 × 10^-6 Ω cm and 1.9 × 10^-6 Ω cm
• The mechanical working of the wire which makes it hard drawn makes the wire harder by breaking the crystal structure into many more tiny crystals.
• This hinders the motion of the walls of the tiny crystals so the wires behave as a harder material but the increased number of crystal walls also hinders the free movement of the electrons and thus driving up the resistivity.