Question

A closely wound solenoid $80cm$ long has $5$ layers of winding of $400$ turns each. The diameter of the solenoid is $1.8cm$. If the current $8.0A$ flows in it , the magnitude of magnetic field inside the solenoid near its centre will be

• A. $8\pi \times {10}^{-3}T$
• B. $6\pi \times {10}^{-3}T$
• C. $4\pi \times {10}^{-3}T$
• D. $3\pi \times {10}^{-3}T$

Answer 1

The correct option is A $8\pi \times {10}^{-3}T$

$\ell =80cm$
$N=5\times 400$ turns $=2000$ turns
$n=\frac{2000}{80}=2500$ turns/m
$i=8A$
$B={\mu }_{0}ni=4\pi \times {10}^{-7}\times 2500\times 8$
$=8\pi \times {10}^{-3}T$