Question

A copper wire $3$ mm in diameter is rounded about a cylinder whose length is $1.2$ m and diameter is $10$ cm 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

The correct option is A $125.6m$

Number of turns of the copper wire
$=\frac{lengthofcylinder}{Diameterofwire}$
$=\frac{1.2m}{3mm}$
$=\frac{1200m}{3mm}$
$=400cm$
$\therefore$The length of the wire in $400$ turn
$=2\pi rn$
$=2\times 3.14\times 10\times 400$
$=12560$cm
$=125.6m$