How can you know if there is current in a conductor without using an ammeter?

There is a magnetic field around the conductor through which the current flows, and if there is a magnetic needle next to it, it will rotate along the magnetic lines. There is no magnetic field around a conductor through which no current flows, and the arrow remains stationary.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.