[2019 DSE] Physics 物理 操題區

仆街 淨係識mechanics

小事，唔洗

想問下右手豎起隻手指公嗰條rule
係咪手指公可以係current or b-field?
即係手指公係current既時候，其他手指轉嗰個方向就係b-field既方向
當手指公係b-field既時候，其他手指轉嗰個方向就係current既方向
係咪咁？

想問下右手豎起隻手指公嗰條rule
係咪手指公可以係current or b-field?

Some people use thumb for current or b-field

即係手指公係current既時候，其他手指轉嗰個方向就係b-field既方向
當手指公係b-field既時候，其他手指轉嗰個方向就係current既方向
係咪咁？

yes, that is correct.

thanks
電好難

想問下幾時用right hand grip rule幾時用左手？

想問下上面巴打post嗰題
洗唔洗consider埋以下紅色框框住嗰個region?

如果要,咁應該係x定o ??

點解個cwsham notes 開出黎變左亂碼

其實唔難，有D 人係亂咗就覺得難，你如果驚，就用一種記法唔好俾自己更亂，lenz law 嘅原理係conservation of energy, 你加energy 入呢一個系統，呢個系統會做出反應，就係會返抗呢個energy 增加，相反，你要從系統抽energy 水，呢個系統就唔卑你抽，會吸返來甘解。

同埋想問下個b-field會去到幾遠?
即係會有一個特定既距離，即係咁：

定係會去到無限遠，即係咁：

咁呢個region應該係x定o?

唔洗考慮，重點係rectangular wire 里邊

red rectangle that you drawn is o, which mean magnetic field(flux) is going out of the paper.

X mean, magnetic field is into the paper.

開到啦

我意思係根據欲拒還迎條rule
紅色個region應該係o定x?

I will do a simple summary.

-------------------------------
| x x x x |
| x x x x |
| x x x x |
| x x x x |
| x x x x |
|__________________|

suppose this is rectangular wire loop, you only consider the magnetic field that is inside the loop, no need to consider magnetic field outside of the loop. because magnetic field generate by current is a circular loop itself, outside of the rectangular loop you will get this.



o o o o o o o o o o o o o o
__________________ o
| x x x x | o
| x x x x | o
| x x x x | o
| x x x x | o
| x x x x | o
|__________________| o
o o o o o o o o o o o o o o

但個長方形行緊去條wire度喎
咁應該係當佢多左o定多左x?
如果就咁諗左邊應該係當佢多左o
但諗埋右邊既話x又會抵銷番d o

睇唔明...

Lm