Question

A long solenoid with $40$ turns per cm carries a current of $1A$. The magnetic energy stored per unit volume is ___________ $J/m^3$.

• A. $3.2\pi$
• B. $32\pi$
• C. $1.6\pi$
• D. $6.4\pi$

Answer 1

Answer: (A)

$3.2\pi$

Given : $I=1A$

Number of turns per unit length, $n=40$ turns per cm $=4000$ turns per m

Energy stored per unit volume, $u=\frac{{\mu }_o{n}^2{I}^2}{2}$

$\therefore$ $u=\frac{4\pi \times {10}^{-7}\times (4000{)}^2\times 1^2}{2}=3.2\pi$ $J/m^3$