* Electromagnetism: A fundamental principle in physics is that moving electric charges create magnetic fields. This is the basis of electromagnetism.

* Compass Needle: A compass needle is a small magnet. It aligns itself with the Earth's magnetic field, pointing north.

* Wire with Current: When electricity flows through a wire, it creates a magnetic field around the wire. The direction of this magnetic field depends on the direction of the current flow.

* Interaction: The magnetic field created by the current in the wire interacts with the magnetic field of the compass needle. When the current direction is reversed, the magnetic field around the wire also reverses direction. This causes the compass needle to shift and point in a different direction.

In simpler terms: Think of the wire as a tiny magnet when current flows through it. When you reverse the current, you're essentially flipping the tiny magnet, causing the compass needle to react accordingly.