Question

A current I is passed through a solenoid of n turns per unit length. What is the magnetic filed inside the solenoid ?

• A. 0
• B. ${\mu }_{0}nI$
• C. ${\mu }_{0}I$
• D. ${\mu }_0{n}^{2}I$

Answer 1

The correct option is B ${\mu }_{0}nI$

Magnetic field outside the solenoid is zero. Consider an Ampere loop going from inside the solenoid across the length to the outside, thus enclosing one edge along the solenoid surface.

From Ampere's law,

${\mu }_{0}NI=B\left(L\right)$
$B=\frac{{\mu }_{0}NI}{L}$
$B={\mu }_{0}nI$