Question

a conductor of resistance 3 ohm is stretched uniformly till its length is doubled the wire is now bent in the form of an equilateral triangle the effective resistance between the ends of any side of the triangle is

Answer 1

heya friend!!☺☺
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here's your answer!!☺☺
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If you double the length of the conductor, then its cross-sectional area must become half of its original value, since volume=area× lenght , is constant. 
Therefore, we can say that
R'=p×4l/A =4R°= 4×3ohm =12 ohm


Now your wire is bent such that each side has a resistance 4 ohms, since the resistance is divided uniformly. 
Now if you make a diagram, you'll see that between vertices, there is an arrangement of two 4 ohms in series connected in parallel with another 4 ohm resistor. The net resistance becomes

8*4/(8+4) = 8/3 ohms. 

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hope it helps you!!☺☺