如何應用弗林明左手定則找出 -- 在電場和磁場中的輻射軌跡？？

I am not sure the radiation you refer to are alpha particle, beta particle and gamma radiation or not. So in this question, I only focus on these three common radiation.

The nature of alpha particle is positively charged; beta particle is negatively charged; and gamma radiation is neutral.

For radiation in an electric field, there is no need to use Fleming's left hand rule to determine the path of radiation. As gamma ray is neutral, it will not deflect in the electric field so it travels in a straight path in its initial direction. Alpha particle is positively charged so it will deflect to the negative pole of the field. Beta particle is negatively charged and it bends to the positive pole of the field.

For radiation in a magnetic field, gamma ray also travels in straight path without deflection. To determine the path of alpha and beta radiation, Fleming's left hand rule can be used. The second finger points to the direction of magnetic field. The middle finger points to the direction of current flow. As alpha particle is positively charged, the current direction is the same as the direction of movement of the particle. However, beta particle is negatively charged so the direction of current is opposite to the movement of the particle. The magnetic field and current direction are known so we can determine the direction of the magnetic force. The thumb points to the direction of the magnetic force and the path of alpha and beta particles follow the direction of force.

Please note that the direction of current, magnetic field and magnetic force are perpendicular to each other.

拇指、食指和中指分別係F,B和I
F係FORCE
B係B-field(magnetic field)
I係current

用個陣可以先用食指指向同磁場一個方向
然後轉動手腕將中指指向同電場一個方向
拇指就會指向力的方向