Two wires of the metal have the same length but their cross-sections are in the ratio 3:1 They are joined in series: The resistance of the thicker wire is $ 10 \Omega $ . The total resistance of the combination will be
$ R_1 = { \delta l \over 3 } = 10 \Omega , R _2 ={ \delta l \over 1} = 30 \Omega $ $ Rs = R_1 + R_2 = 10 \Omega + 30 \Omega = 40 \Omega $

