To test whether a material is a superconductor, a scientist decides to make a ring out of the material and then to see whether a current will flow around in the ring with no steady energy input. a) Explain how a magnet could be used to initiate the current. b) At some later time, how could the scientist check to see whether the current is still flowing in the ring but without touching the ring?

Faraday's law explains that when a conductor is exposed to a changing magnetic field, an electromotive force is induced, creating a current. In our case, the conductor is the superconducting ring. To initiate the current, move the magnet towards the ring, so the magnetic field lines pass through it. Then as you move the magnet away from the ring, the magnetic field lines continue to pass through the ring. This changing magnetic field generates an electromotive force (EMF) in the ring, causing a current to flow in it.

To check if the current is still flowing in the superconducting ring without touching it, we can use the principle of electromagnetic induction. If a current is still flowing in the ring, a magnetic field will be present around the ring. This can be tested using another coil or a Hall effect sensor. 1. Move the coil or Hall effect sensor close to the superconducting ring, and record the magnetic field measurements. 2. Then, move the coil or Hall effect sensor away from the superconducting ring. The difference in the magnetic field measurements when the sensor is close to and far from the ring indicates the presence of a magnetic field created by the current in the ring. If the magnetic field measurements don't change as the coil or Hall effect sensor is brought close to the ring, it indicates that the current is not flowing in the ring. By following these steps, the scientist can initiate a current in a superconducting ring using a magnet and also check whether the current is still flowing without touching the ring.