How does the resistance of a wire change when: a) its length is tripled? b) its diameter is tripled? its material is changed to one whose resistivity is three times?

We know that,

R = ρl/A

1. l becomes 3l R’ = ρ3l/A

= 3R

Therefore, resistance gets tripled

1. d becomes 3d R = ρl/A

R = ρl/πr2

= ρl/π(d/2)2 R’ = R/9

Therefore, resistance becomes 1/9th

1. ρ = 3ρ R’ = 3ρl/A

= 3R

Therefore, resistance becomes 3 times.