1. Applied Electricity and Magnetism
ECE 3318
Applied Electricity and Magnetism
Spring 2017
Prof. David R. Jackson
ECE Dept.
Notes 29

2. Biot-Savart Law a) Volume current b) Surface current r
Please see the textbooks for a derivation.
a) Volume current
b) Surface current r

3. Biot-Savart Law (cont.)
c) Line current (wire)
Note on notation:
Rule:
The contour C is in direction of the I arrow
(i.e., the reference direction for the current).
(This determines the starting point A and the ending point B.)

4. Example
Find H
Infinite line current

5. Example (cont.)
Hence we have:

6. Example (cont.) I

7. Example (cont.)
Note:
Hence we have or

8. Example (cont.) Summary
Note: This agrees with the answer obtained by Ampere’s law.

9. Example Find H Circular loop of current
Note: This problem cannot be solved using Ampere’s law!

10. Example (cont.) so

11. A prime is not necessary on unit vector z.
Example (cont.)
Note:
A prime is not necessary on unit vector z. so

12. Example (cont.)
Summary x y z a
r = (0,0,z) I

13. Example (cont.) r = (0,0,z) As z  : I z a y x
This explains why it is difficult to achieve a significant range in a wireless charging system: