A wire's length is increased by 25%. What % will the resistance be increased.

R 1/L

Rf/Ri = Li/Lf where i and f refers to initial and final values respectively.

(Lf - Li)/Li = 0.25

Hence Li/Lf = 1/1.25.

Therefore,

Rf/Ri = 1/1.25

Rf = 0.8Ri

(Rf - Ri)/Ri = -0.20.

Hence resistance will decrease by 20%.

Regards,

Team,

TopperLearning.