Currents create magnetic fields, leading to a third variable, magnetic flux, which characterises the field's strength.
电流产生了磁场，导致第三个变量的产生-磁通量，它表示磁场的强弱。
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"We've always known that the Earth's magnetic field is variable, constantly evolving in time," Raymond said.
“众所周知地球的磁场是变化的，无时无刻不在变化”雷蒙德教授说。
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More precisely it tells you that what you might have learned about electric fields deriving from electric potential becomes false if you have a variablemagnetic field.