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?

To initiate a current in the ring made of the material, we can make use of electromagnetic induction, which is governed by Faraday's law of magnetic induction. Faraday's law states that an electromotive force (EMF) is induced in a closed loop of wire when there is a change in magnetic flux through the loop. Mathematically, it can be written as: EMF \(= -\dfrac{d\Phi}{dt}\) where \(\Phi\) is the magnetic flux and \(t\) is time. In order to initiate a current in the ring, the scientist can move a magnet towards or away from the ring, or alternatively change the orientation of the magnet relative to the ring. This will cause a change in the magnetic flux through the ring, and according to Faraday's law, an EMF will be induced in the ring. If the ring is made of a material that is a superconductor, the induced current will flow without any resistance and therefore will not require a steady energy input.

At a later time, the scientist can check if the current is still flowing in the ring without touching it, by making use of electromagnetic induction and a device called a galvanometer. A galvanometer is a sensitive instrument used to measure the presence of small electric currents. To measure the presence of current in the ring, the scientist can perform the following steps: 1. Prepare a separate closed loop of wire or a coil connected to a galvanometer. 2. Slowly move the loop of wire or coil towards or away from the ring, or alternatively change the orientation of the loop relative to the ring. 3. Observe the galvanometer's needle or reading. If there is still a current flowing in the ring, moving the closed loop of wire or coil near the ring will change the magnetic field around the ring, leading to a change in magnetic flux through the wire loop or coil. This change in magnetic flux will induce an electromotive force (EMF) in the loop of wire or coil, as per Faraday's law. If an EMF is induced in the loop of wire or coil connected to the galvanometer, the galvanometer's needle will register a deflection or a reading, suggesting that a current is still present in the ring even at a later time. This would confirm that the material is a superconductor, as there is no steady energy input yet the current still flows without resistance.