Challenging magnetism

Case I: When r <= R (i.e. the point is inside the ring OR on the circumference)

圖片參考：http://i117.photobucket.com/albums/o61/billy_hywung/Apr09/CrazyEM1.jpg


圖片參考：http://i117.photobucket.com/albums/o61/billy_hywung/Apr09/CrazyEM2.jpg


圖片參考：http://i117.photobucket.com/albums/o61/billy_hywung/Apr09/CrazyEM3.jpg

Case II: When r > R (i.e. the point is outside the ring)

圖片參考：http://i117.photobucket.com/albums/o61/billy_hywung/Apr09/CrazyEM4.jpg

Note: Though the expressions are the same for both case, for case I, R + r cos θ is always positive and therefore all fields contributed by any small length of wire segment are in the same direction while for case II, as stated above, dB changes sign at some value of θ and hence after integration, the field value should be smaller than that of case I.

2009-04-08 16:58:15 補充：
半年後你同 Audrey Hepburn 都會識做呢題!!!

2009-04-15 12:04:05 補充：
http://i117.photobucket.com/albums/o61/billy_hywung/Apr09/CrazyEM7.jpg

http://i117.photobucket.com/albums/o61/billy_hywung/Apr09/CrazyEM8.jpg

張遼好勁!