Ampere's Law Formula

Ampere’s law came to existence in 1826. The law talks about the sum of the magnetic field across a closed hoop which is carrying current. Ampere’s law can be useful when measuring high 

degree of symmetry for magnetic fields with current distributions.

Ampere’s Law Formula

\(\oint \vec{B}\vec{dl}=\mu _{0}I\)

Notations Used In Ampere’s Law Formula

  • B is the magnetic field
  • L is the infinitesimal length
  • I is the current flowing through the closed-loop
  • μ is the permeability

Solved Example

Question 1: Compute the magnetic field of a long straight wire that has a circular loop with a radius of 0.05m. 2amp is the reading of the current flowing through this closed loop.



R = 0.05m

I = 2amp

μ0 = 4π×10-7N/A2

Ampere’s law formula is

\(\oint \vec{B}\vec{dl}=\mu _{0}I\)

In the case of long straight wire

\(\oint \vec{dl}=2\pi R=2\times 3.14\times 0.05=0.314\)

\(B\oint \vec{dl}=\mu _{0}I\)

\(\vec{B}=\frac{\mu _0I}{2\pi R}\)

\(\vec{B}=\frac{4\pi \times 10^{-7}\times 2}{0.314}=8\times 10^{-6}\,T\)

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