Question

$A$ $90 \,cm$ long solenoid has six layers of windings of $450$ turns each. If the diameter of solenoid is $2.2\, cm$ and current carried is $6 \,A$ , then the magnitude of magnetic field inside the solenoid, near its centre is

• A. $50\pi\, G$
• B. $60\pi\, G$
• C. $72\pi\, G$
• D. $80 \pi\, G$

Answer 1

Answer: (C)

For six layers of windings the total number of turns = $6 \times 450 = 2700$
Now number of turns per unit length
$n=\frac{N}{l}=\frac{2700}{90\times10^{-2}}=3000$
Then the field inside the solenoid near the centre
$B=\mu_{0}nI =4\pi\times10^{-7}\times3000\times6$
$=72\pi\times10^{-4}\,T $
$=72\pi\,G$