A copper wire has a diameter of 0.5mm and a resistivity of 1.6 ohm cm.How much of this wire would be necessary to make a 10 ohm coil?
we know that
R = Ïl/A
or
l = AR/Ï
where
l = length of the wire = to be found
A = area of cross-section = π(d/2)2 = 3.14x(0.05/2)2 = 1.96 x 10-3 cm2
Ï = resistivity = 1.6 ohm.cm
R = resistance = 10 ohm
so,
l = (1.96 x 10-3 x 10) / 1.6
or
l = 0.01225 cm = 0.125 mm