CBSE Class 10 Answered
We have to completely wrap the CSA of cylinder. Since in one wrap of copper wire of 3 mm diameter, a 3 mm height of 12 cm heighted cylinder is consumed.
Hence to find how many such wraps make up the required 12 cm, we divide 12 cm/3 mm = 120 mm/3 mm = 120 wraps or rounds.
The length in one wrap = πD = 3.14x10 cm = 31.4 cm.
Total length of wire = 120x31.4 = 3768 cm
The volume of the wire = cross sectional areaxlength = 3.14x0.32x3768/4 = 266.21 cm3
Mass of wire = densityxvolume = 8.88x266.21 = 2364 gm = 2.4 kg.