free electron

例句：

1. 1.Free electrons can be used to create a strong magnetic field.
   自由电子可以用来产生强大的磁场。
2. 2. The free electron gas is responsible for the electrical conductivity of semiconductors.
   自由电子气体负责半导体的电导性。
3. 3.In the early days of electronics, scientists believed that free electrons were essential for transistors.
   在电子学初期，科学家们认为自由电子对于晶体管至关重要。