2018 · Q33
Two metallic wires made from copper have same length but the radius of wire 1 is half of that of wire 2. The resistance of wire 1 is R. If both the wires are joined together in series, the total resistance becomes:
General KnowledgePhysics
- A2R
- BR/2
- C5R/4
- D3R/4
Explanation
Resistance R = ρL/A with A = πr². Wire 1's radius is half of wire 2's, so its cross-sectional area is one-fourth and its resistance is four times wire 2's. Given wire 1's resistance is R, wire 2's is R/4. Joined in series, the total resistance is R + R/4 = 5R/4.