2017 · Q28
A copper wire of radius r and length l has a resistance of R. A second copper wire with radius 2r and length l is taken and the two wires are joined in a parallel combination. The resultant resistance of the parallel combination of the two wires will be 5
General KnowledgePhysics
- A5R
- B5/4 R
- C4/5 R
- DR/5
Explanation
Resistance is proportional to length/area. Doubling the radius quadruples the area, so the second wire's resistance is R/4. In parallel: (R × R/4)/(R + R/4) = R/5. Hence D.