Question Video: Recognizing That a Stationary Bar Magnet Induces a Current in a Moving Copper Ring | Nagwa Question Video: Recognizing That a Stationary Bar Magnet Induces a Current in a Moving Copper Ring | Nagwa

# Question Video: Recognizing That a Stationary Bar Magnet Induces a Current in a Moving Copper Ring Physics • Third Year of Secondary School

Each of the following diagrams shows a copper ring moving near to a stationary bar magnet. In each case, the red arrow shows the direction in which the copper ring is moving. In which case, if any, will no current be induced in the copper ring? [A] Diagram A [B] Diagram B [C] Diagram C [D] Diagram D [E] A current will be induced in the ring in all of the cases shown.

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### Video Transcript

Each of the following diagrams shows a copper ring moving near to a stationary bar magnet. In each case, the red arrow shows the direction in which the copper ring is moving. In which case, if any, will no current be induced in the copper ring? (A), (B), (C), (D), or (E) a current will be induced in the ring in all of the cases shown.

To answer this question, we need to determine whether a current is induced in the ring in each of these scenarios. In each option, the bar magnet is stationary and the copper ring is moving. Let’s start by clearing some space on screen and reminding ourselves about electromagnetic induction.

Imagine a stationary copper ring, on its own, with no magnets around it. The ring isn’t connected to any kind of circuit, and there’s nothing else near the ring. So there is no current in this ring, because there is nothing that could cause the charges in the ring to flow. Now consider what would happen if we placed a stationary bar magnet near to the ring. In this case, there is still no current in the ring. But some of the bar magnet’s magnetic field lines now pass through the ring, like this. If the ring started to move, the magnetic field that passes through the ring would change. When the ring is in a different position, the number of magnetic field lines that pass through the ring might be different, or the direction of the field lines might be different. If either of these things change, the magnetic field passing through the ring changes.

So, when the ring is moving, the magnetic field that passes through the ring is changing. If the ring was stationary and the bar magnet was moving, this would also cause the magnetic field that passes through the ring to change. The change in magnetic field creates a current in the ring. This process is called electromagnetic induction. When the ring moves, the magnetic field that passes through the ring changes, and a current is induced in the ring.

To answer this question, we need to work out whether any of the options given show a case in which no current will be induced in the ring. For this to be the case, we would need both the ring and the magnet to be stationary. But we know that each of the diagrams shows a ring that is moving near to a bar magnet. So a current will be induced in all of the rings shown. Note that it doesn’t matter which direction the ring is moving in. As long as the ring is moving, a current will be induced in the ring.

So a current is induced in the ring in all the cases we have been given. The correct answer is therefore option (E).

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