15. 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 A.2R B.R/2 C.5R/4 D.3R/4
Option C Solution: So, resistance of Wire 2 is R/4 as radius is half of wire 1, so area would be 4 times of wire 1. Now for resistance in series. R= R1 + R2. Therefore, Final R= R + R/4 = 5R/4
