Yahoo 知識+ 將於 2021 年 5 月 4 日 (美國東岸時間) 停止服務。從 2021 年 4 月 20 日 (美國東岸時間) 起,Yahoo 知識+ 網站將轉為僅限瀏覽模式。其他 Yahoo 資產或服務,或你的 Yahoo 帳戶將不會有任何變更。你可以在此服務中心網頁進一步了解 Yahoo 知識+ 停止服務的事宜,以及了解如何下載你的資料。

匿名 發問於 科學及數學其他 - 科學 · 8 年前

direction problem.

A unfiorm electric field of 1.86 X 10^4 V/m and a uniform magnetitc field of 2.62 X 10^-3 T are oriented at right angles to each other in an empty region of space.

a) if a beam of electrons passes through these fields at right angles to both of them what is the speed of the electrons if they experience no deflection?

b) if the electrons are traveling in the +x direction of a right - handed ( x, y, z) coordinate system, and the magnetic field points in the +y direction, what is the direction of the electric field?

i dont know how to do b..that is not +z direction

1 個解答

  • 天同
    Lv 7
    8 年前

    (b) The beam of electrons are moving in the +x direction, thus the direction of conventional current is flowing in the -x direction.

    Since the magnetic field lines are pointing in the +y direction, by using Fleming's Left Hand Rule (Motor Rule), the magnetic force is acting at the -z direction.

    Hence, the electric force acting on the electrons should be pointing at the +z direction in order to balance the magnetic force. Therefore, the electric field lines act in the -z direction, as electrons go against the electric field lines.