1. Lecture 24: FRI 13 MAR Ch.29.5–6: Ampere’s Law Physics 2102
Jonathan Dowling
Lecture 24: FRI 13 MAR
Ch.29.5–6: Ampere’s Law
André Marie Ampère
(1775 – 1836)

2. Ampere’s law: Closed Loops
The circulation of B
(the integral of B scalar ds) along an imaginary closed loop is proportional to the net amount of current traversing the loop.
Thumb rule for sign; ignore i3
If you have a lot of symmetry, knowing the circulation of B allows you to know B.

3. e n c C a l u t i o f . W r h g s d w A m p v b

4. Solenoids

6. Magnetic Field in a Toroid “Doughnut” Solenoid
Toriod Fusion Reactor:
Power NYC For a Day on a Glass of H2O

7. Magnetic Field of a Magnetic Dipole
A circular loop or a coil currying electrical current is a magnetic dipole, with magnetic dipole moment of magnitude =NiA. Since the coil curries a current, it produces a magnetic field, that can be calculated using Biot-Savart’s law:
All loops in the figure have radius r or 2r. Which of these arrangements produce the largest magnetic field at the point indicated?

8. Neutron Star a Large Magnetic Dipole