Notes for PH 113 (Moloney)

• Biot-Savart law: dBp = uo I/(4 pi) dl x r/r^3
• dBp is an element of magnetic field created at point P
• dl always follows the current I
• r points from dl to P
• applications which we did:
• B at center of a circular loop of current
• B on the axis of a circular loop of current, a distance x from the center
• B at a distance y from a long straight wire

• Ampere's law: uo I = integral of B dot dl along a curve c
• I is the current 'enclosed' by the curve c
• to be enclosed, I must penetrate the area enclosed by c
• dl does NOT follow the current.
• dl follows the mathematical curve c
• with this, we calculated
• B at a distance y from a long straight wire carrying current I
• B inside a long wire of radius R (a 'fat' wire), and outside this wire