Which law relates magnetic fields to the currents that produce them?

Which law relates magnetic fields to the currents that produce them?

• A. Faraday's Law
• B. Ampere's Law
• C. Gauss's Law
• D. Ohm's Law

Answer: (B)

Ampere's Law describes how magnetic fields arise from currents. In magnetostatics, a steady current creates a magnetic field whose line integral around a closed loop is proportional to the current that threads the loop: ∮ B · dl = μ0 I_enc. This ties the strength and direction of the magnetic field directly to the amount and direction of current, with the right-hand rule giving the field direction around a conductor. The full Maxwell-Ampere form adds the displacement current term for changing currents, but the essential idea is that current produces the magnetic field. The other concepts don’t capture that direct link. Faraday’s Law connects changing magnetic flux to an induced electric field (EMF), not the current-generated magnetic field. Gauss’s Law for magnetism states that there are no magnetic monopoles and describes the flux of B through a surface, not how currents produce B. Ohm’s Law relates voltage, current, and resistance in a circuit, not the magnetic field produced by current.

Ampere's Law describes how magnetic fields arise from currents. In magnetostatics, a steady current creates a magnetic field whose line integral around a closed loop is proportional to the current that threads the loop: ∮ B · dl = μ0 I_enc. This ties the strength and direction of the magnetic field directly to the amount and direction of current, with the right-hand rule giving the field direction around a conductor. The full Maxwell-Ampere form adds the displacement current term for changing currents, but the essential idea is that current produces the magnetic field.

The other concepts don’t capture that direct link. Faraday’s Law connects changing magnetic flux to an induced electric field (EMF), not the current-generated magnetic field. Gauss’s Law for magnetism states that there are no magnetic monopoles and describes the flux of B through a surface, not how currents produce B. Ohm’s Law relates voltage, current, and resistance in a circuit, not the magnetic field produced by current.