Two wires of same 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

Options

A. `40 Omega`
B. `40/3 Omega`
C. `5/2 Omega`
D. `100 Omega`

Answer

A

Explanation

`A_(1) = 3A, A_(2) = A`
`R prop 1/A`
`rArr R_(1)/R_(2) = 1/3`
`R_(1) 10 Omega, R_(2) = 30 Omega`
`R_(eq) = 40 Omega`