Amperes circuital law is a fundamental law in classical electromagnetism that relates the circulation of a magnetic field around a closed loop to the electric current passing through the loop. The law was first derived by James Clerk Maxwell using hydrodynamics in his 1861 published paper "On Physical Lines of Force". In its modern form, the law is sometimes called the Ampere-Maxwell law, which is one of Maxwells equations that form the basis of classical electromagnetism. The equation explaining Amperes law is given by the line integral of the magnetic field surrounding a closed loop equals the number of times the algebraic sum of currents passing through the loop. The left side of the equation describes that if an imaginary path encircles the wire and the magnetic field is added at every point, then it is numerically equal to the current encircled by this route, indicated by Ienc. The law is useful in calculating magnetic fields due to symmetric situations.