H H   Sources of Magnetic Fields
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Dr. Walter Lewin (MIT)
14b_BiotSavartLaw.mov (106 MB)

Magnetism Closeup

What does this mean to me?

A classical description would suggest that the emergence of magnetism in matter is manifested by the electron orbiting the nucleus. Hence, an electron current produces a magnetic field. Quantum Physics provides a more precise explanation based upon the orbital and spin properties of electrons in atoms. Our understanding of electronic behavior has given us the ability to produce ultrasensitive and micromagnetic storage devices. Who's interested now?

Mechanical Universe

The Magnetic Force between two parallel conductors

Ampere's Law

This is the same value obtained from the Biot-Savart Law

Is Ampere's Law valid for all closed paths surrounding a conductor?


What makes Ampere's Law useful?

Mechanical Universe

Is the Magnetic Field inside a toroid uniform?
Problem #27 would be a great physics demonstration

Conclusion: There is a magnetic field due to the current in the wire (H). And, there is a magnetic field due to the Magnetization (M) of the material.