Question

a wire of resistance R ohm is dauble on it.calculate new resistance.​

Answer 1

We consider wire is doubled on it means to fold the length of wire. It means its length will get half and area of cross section will get doubled.

∴ Let the resistance of the wire originally 'R'' of length 'L' and area of cross-section 'A' with resistivity of material is 'p',

Then

R'= p l/A = R ohm

Now, for new arrangement,

p" = p

l"= l / 2

A"= 2A

Thus, 

R"= p"l"/A"= p"(l"/2) ÷ 2A = 1/4 (p l / A) = 1/4.R1 = 1/4Ω.