Ampere's Circuital Law states that the magnetic field \( B \) around a closed loop is proportional to the current passing through the loop. The law is expressed mathematically as:
 
 \[
 \oint_{\text{loop}} \mathbf{B} \cdot d\mathbf{l} = \mu_0 I_{\text{enc}},
 \]
 
 where:
 - \( \oint_{\text{loop}} \mathbf{B} \cdot d\mathbf{l} \) is the circulation of the magnetic field around the loop,
 - \( \mu_0 \) is the permeability of free space,
 - \( I_{\text{enc}} \) is the current enclosed by the loop.