Question

 A tightly-wound, long solenoid having 50 turns/cm, carries a current of 4.00 A. Find the magnetic 

intensity H and the magnetic field B at the centre of the solenoid.

Answer 1

(a)

$$H=\dfrac{NI}{L}=nI=50\cdot10^{2}\ \dfrac{turns}{m}\cdot4\ A=2\cdot10^4\ \dfrac{A}{m}.$$

(b)

$$B=\mu_0H=4\pi\cdot10^{-7}\ \dfrac{Tm}{A}\cdot2\cdot10^4\ \dfrac{A}{m}=0.025\ T=25\ mT.$$