The direction of eddy current is determined by Lenz's law. Lenz's law is one of the fundamental principles of electromagnetism, which states that the direction of an induced current in a conductor is such that it opposes the change that caused it. In other words, the direction of the eddy current is opposite to the direction of the change in the magnetic field that induces it.

Lenz's Law:
Lenz's law can be summarized with the following key points:

1. Opposing Change: Lenz's law states that an induced current will flow in such a direction that it opposes the change that is causing it. This means that if there is an increase in the magnetic field, the induced current will flow in a direction to create a magnetic field that opposes the increase. Similarly, if there is a decrease in the magnetic field, the induced current will flow in a direction to create a magnetic field that opposes the decrease.

2. Conservation of Energy: Lenz's law is a consequence of the law of conservation of energy. When a change in magnetic field occurs, work is done to induce the current. Lenz's law ensures that the work done to induce the current is not lost but is conserved.

3. Fleming's Right-hand Rule: To determine the direction of the induced current, Fleming's right-hand rule can be used. If the right-hand thumb points in the direction of the inducing magnetic field, the curled fingers indicate the direction of the induced current.

4. Eddy Currents: Eddy currents are circular currents that are induced in a conductor when it is exposed to a changing magnetic field. The direction of these eddy currents is determined by Lenz's law, opposing the change in the magnetic field.

5. Applications: The direction of eddy currents plays a crucial role in various applications. For example, in electromagnetic braking systems, the eddy currents are induced in a metal disc by a changing magnetic field, which generates a force opposing the motion and helps in bringing the object to a stop.

In summary, Lenz's law governs the direction of eddy currents and ensures that the induced current opposes the change in the magnetic field. This law is based on the principle of conservation of energy and has various practical applications.