A uniform wire of resistance 20 ohm having resistance 1 Ω/m is bent in form of a circle as shown in fig. If the equivalent resistance  between M and N is 1.8 Ω, then the length of the shorter section is

Let the resistance of the shorter part MN be x. Total resistance is 20. Hence the resistance of longer MN part will be (20 -x). With respect to M and N, the portions are connected in parallel. Hence∴ Req=(20−x)×x(20−x)+x=1⋅8Solving, we get x = 2mThe resistance is 1Ω/ m and hence the length of shorter part MN= 2 x 1= 2m