Question

An aluminium rod of length 3.14 m is of square cross-section 3.14 × 3.14 mm². What should be the radius of 1 m long another rod of same material to have equal resistance

• A. 2 mm
• B. 4 mm
• C. 1 mm
• D. 6 mm

Answer 1

Answer: (C)

1 mm

Answer 2

By using $R = \rho.\frac{l}{A}$ ⇒ l ∝ A ⇒ $\frac{3.14}{1} = \frac{3.14 \times 3.14 \times 10^{- 6}}{\pi \times r^{2}}$ ⇒ r = 10^–3 m = 1 mm