# 8. A closely wound solenoid 80 cm long has 5 layers of windings of 400 turns each. The diameter of the solenoid is 1.8 cm. If the current carried is 8.0 A, estimate the magnitude of B inside the solenoid near its centre.

The magnitude of the magnetic field at the centre of a solenoid of length l, total turns N and carrying current I is given by

$B=\frac{\mu _{o}NI}{l}$ , where $\mu _{o}$ is the permeability of free space.

In the given question N= number of layers of winding$\times$number of turns per each winding

N=5$\times$400=2000

I=8.0 A

l=80 cm

$B=\frac{4\pi \times 10^{-7}\times 2000\times 8}{0.8}$

$\\B=2.51\times10^{-2} T$

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