It is alternating current that explains the soft iron bar, so there are many changing magnetic fields around the bar to produce electric fields. When the conductor of the diode bead is put into an electric field, the electrons move to generate current, and the diode emits light. Red diodes have smaller electrons and require lower voltage, so red lights up first. The change of brightness is related to the magnetic induction intensity, which is related to the distance, so it gets brighter as you go down.

It is the property that magnets repel each other and opposites attract each other, which makes magnets have the ability of defying gravity, that is, "magnetic levitation". Scientists apply the principle of "magnetic levitation" to the railway transportation system, which makes the train completely off the track and float, becoming a "wheelless" train with a speed of more than hundreds of kilometers per hour. This is the so-called "maglev train", also known as "magnetic cushion car".

Extended data:

The magnetic suspension technology system consists of rotor, sensor, controller and actuator, in which the actuator includes electromagnet and power amplifier. Assuming that the rotor is disturbed downward at the reference position, it will deviate from its reference position, and then the sensor detects the displacement of the rotor from the reference point;

As a controller, the microprocessor converts the detected displacement into a control signal, and the power amplifier converts the control signal into a control current, and the control current generates a magnetic force in the actuator magnet, thereby driving the rotor back to the original equilibrium position. Therefore, no matter whether the rotor is disturbed downward or upward, the rotor can always be in a stable equilibrium state.

Baidu encyclopedia-magnetic levitation technology