A uniform wire resistance `20 Omega` having resistance `1 Omega ` is bent in the forms of a circuit if the equal - valent resistance between A and B is `1.8 Omega ` then length of the shorter section is

Options

A. `1.8 m`
B. `2 m`
C. `3.6 m`
D. `4 m`

Answer

b

Explanation

Let resistance of shorter part `AB` be `x` the total resistance is `20 Omega` the resistance of longer `AB` part is `(20- x)` between point A and B the two resistance `x` and their equivalent resistance in
`R_(eq) = ((20 - x) xx x)/((20 - x) xx x) = 1.8`
On solving get `x = 2 Omega`
Thus, length of the shorter section `= 2 xx 1 = 2m`