Answer:
RA / RB = 8.33
Step-by-step explanation:
The resistance in terms of area is given by the following equation:
R = d * L / A
the density being the same in both cases, L the length, which is the same in both conductors and A the area that it does vary.
Now, in the case of conductor A, the area would be:
AA = pi * rA ^ 2
we know that d / 2 = r, therefore:
AA = (pi / 4) * dA ^ 2
Replacing in the resistance formula:
RA = 4 * dA * L / (pi * d ^ 2)
In the case of B we have that the area we want to know is equal to the area on the outside minus the area on the inside
AB = pi * rBo ^ 2 - pi * rBi ^ 2
expressing in diameters:
AB = (pi / 4) * (dBo ^ 2 - dBi ^ 2)
Replacing in R
RB = 4 * d * L / (pi * (dBo ^ 2 - dBi ^ 2))
To know RA / RB we divide these two expressions, the term 4 * d * L is canceled, which is the same in both cases and we are left with:
RA / RB = (dBo ^ 2 - dBi ^ 2) / dA ^ 2
Replacing these values:
RA / RB = (8 ^ 2 - 4 ^ 2) /2.4^2
RA / RB = 8.33