Question

A wire of resistance 20 ohm having length 2m if length will be taken 3 times what will be new resistance?

Answer 1

R=resistivity(rho)*length(l)/A(area of cross sec)

R=20 ohm initially at length l and area of cross sec A

rho is constant since it dosent depends on dimension

hence R∝l/A

new resistance R' when length is increased by 3 times

concept: when u increase length by 3 times area of cross sec will decreases by 3 times

R'=3l/(A/3)

R'=6l/A

R'=6R

hence resistance increases by 6 times

new resistance= 6*20=120 ohms

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