# A copper wire, 3 mm in diameter, is wound about a cylinder whose length is 12 cm, and diameter 10 cm, so as to cover the curved surface of the cylinder. Find the length and mass of the wire, assuming the density of copper to be 8.88 g per cm^{3}

**Solution:**

A figure is drawn to visualize the cylinder.

As we know that the curved surface of the cylinder to be covered with the copper wire, then one round of copper wire will cover the same height of the cylinder as of the width (diameter) of the wire.

Therefore, Length of the wire × diameter the of wire = CSA of the cylinder

Let us find the CSA of the cylinder by using the formula;

CSA of the cylinder = 2πrh, where r and h are the radius and height of the cylinder respectively.

To find the mass of the wire:

Mass = Density × Volume

As the density of the copper is given, we need to find the volume of the wire first.

As the wire is cylindrical in shape

Therefore, Volume of the wire = volume of the cylinder

Let us find the volume of the cylindrical wire by using the formula:

Volume of the cylinder = πr_{1}^{2}h_{1}, where r_{1} and h_{1} are the radius and the length of the cylindrical wire

Height of cylinder, h = 12 cm

Diameter of cylinder, d = 10 cm

Radius of cylinder, r = 10 cm / 2 = 5 cm

Diameter (width) of wire d_{1} = 3 mm = 3 / 10 cm = 0.3 cm

Radius of wire, r_{1} = 0.3 cm/2 = 0.15 cm

Let the length of the wire be h_{1}

Since curved surface of the cylinder to be covered with the wire

Length of the wire × diameter the of wire = CSA of the cylinder

d_{1} × h_{1} = 2πrh

h_{1}= 2πrh/d_{1}

= (2 × 3.14 × 5 cm × 12 cm) / 0.3 cm

= 1257.14 cm

Volume of the wire = volume of the cylinder

= πr_{1}^{2}h_{1}

= 3.14 × 0.15 cm × 0.15 cm × 1257.14 cm

= 88.898 cm^{3}

Density of copper = 8.8 g /cm^{3}

Mass of the copper Wire = Density × volume

= 8.88g / cm^{3} × 88.898 cm^{3}

= 789.41 g

Thus, the length of the wire is 12.57 m and the mass is 790 g (approx.)

**Video Solution:**

## A copper wire, 3 mm in diameter, is wound about a cylinder whose length is 12 cm, and diameter 10 cm, so as to cover the curved surface of the cylinder. Find the length and mass of the wire, assuming the density of copper to be 8.88 g per cm^{3}

### NCERT Solutions for Class 10 Maths - Chapter 13 Exercise 13.5 Question 1 :

A copper wire, 3 mm in diameter, is wound about a cylinder whose length is 12 cm, and diameter 10 cm, so as to cover the curved surface of the cylinder. Find the length and mass of the wire, assuming the density of copper to be 8.88 g per cm^{3}

The length and mass of the copper wire 3 mm in diameter used to wound about a cylinder of length 12 cm and diameter 10 cm are 1256 cm and 790 g respectively