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Anderson Video - EMF Example

Professor Anderson
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Okay, so the next one has a little figure. Let's draw it right here. We've got a ring. Then, there is B field which is pointing out of this ring. Okay? And it says the following: a non conducting plastic hoop is held in a magnetic field that points out of the figure. As the strength of the field increases, so B field is coming out towards you and it's increasing, we need to figure out what's going to happen to the EMF in this loop. Here are some choices: an induced EMF will be produced that causes a clockwise current, no induced EMF will be produced, an induced EMF will be produced that causes a counter-clockwise current, an induced EMF will be produced but no current. Hmm. What do you guys think? You like the last one? Why do you like the last one? Okay. EMF is negative delta phi over delta t. We know what delta phi is, right? It can change B. It could change A, or it can change theta. So, is something changing? Yes. They tell us that B increases. So B increasing means that this is non zero. So, EMF is produced. Now, what we said was: "EMF being produced means that there will be a current generated in this loop." But, you can think of this loop as composed of metal and a resistor. What they tell us is that it is a nonconducting plastic hoop. So if it's plastic, what is R? Approximately? Or, we should say approaching. It's approaching infinity. Right? What is the current that develops? I is equal to v over R which is EMF epsilon over R. The epsilon was non zero, of course, but the resistance is basically infinite. So, you do produce an EMF, but you produce no current. I like the last one as well. Let's click that and submit it. And that is indeed correct. EMF is produced, but no current flows because the resistance is infinite Sara is that okay? All right.