Question

(a) Define resistivity with S.I unit.

(b) A 4 ohm resistance wire is doubted. calculate the new resistance of the wire. ​

Answer 1

Answer:

a) Resistivity can be defined as the resistance of a conducting material per unit length with unit area of cross section. So it SI unit will be. ρ= RA / l.

b)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 = 4Ω

Now, for new arrangement,

p' = p

l' = l / 2

A' = 2A

Thus,  

R' = p' l'/A' = p (l /2) ÷ 2A = !/4 (p l / A) = 1/4R = 1/4 × 4 = 1Ω.

Hope it helps u !!