Question

A copper wire $3mm$ in diameter is rounded about a cylinder whose length is $1.2m$ and diameter is $10cm$., so as to cover the curved surface of the cylinder. The length of the wire is

• A. $125.6m$
• B. $1256m$
• C. $12.56m$
• D. $1.256m$

Answer 1

Answer: (A)

$125.6m$

Curved surface area of wire $=$ CSA of cylinder

$\Rightarrow l\times b=2\pi rh=l\times \frac{3}{10}=2\times \frac{22}{7}\times \frac{10}{2}\times (1.2\times 100)$

$\Rightarrow l=\frac{2\times 22\times 10\times 120\times 10}{3\times 7\times 2}=12571cm\approx 125.7m$