Questions  

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

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a
2m
b
5m
c
1.8 m
d
18 m
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detailed solution

Correct option is A

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

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