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This video is about the induced EMF in a coil that is moving through a magnetic field.

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We'll examine three different moments as the coil moves through the field.

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First, as the coil enters the field. Second, as the coil is entirely inside the field

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and is moving through the field. And finally, as the coil is leaving the field.

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Let's see what happens as the coil starts entering the field.

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Here, we can take two different approaches.

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First, let's use Fleming's right hand rule.

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If you would like to refresh how this rule works, feel free to watch video 11.1.1

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titled induced electromotive force. So in order to find the direction of the induced current,

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point your thumb in the direction of the conductor's motion, so to the right,

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point your index finger in the field direction, so into the screen or page.

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And if you have done this correctly, your middle finger should show the

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direction of the induced current, which here is upwards.

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This is the current induced at the right end of the coil, so here.

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Since the left end of the coil has not yet entered the magnetic field,

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there is no current induced in this section of the coil.

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Since the coil is moving horizontally, and the two longer sides of the coil are horizontal,

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logically, there is no induced current in these two sides either.

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Since the coil can be considered as a closed circuit, the current that is induced at the right

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end of the coil will be able to flow around the coil. Therefore, there is an anticlockwise

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current in the coil, so there is also an induced EMF in the coil.

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Another approach that we can take to show that there is an induced EMF in the coil

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is to use Faraday's law. Here is the equation that expresses this law.

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To revise how this law works, feel free to watch the previous video.

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This law tells us that a changing magnetic flux causes an induced EMF.

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As the coil is entering the magnetic field, magnetic flux through the coil is increasing.

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Since there is a change in magnetic flux, there is an induced EMF in the coil.

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Next, let's see what happens as the coil is passing through the field.

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Once again, we can use Fleming's right hand rule to find the direction of the induced current.

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I won't go through the steps here again, but the big difference in this case

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is that since both the right side and the left side of the coil are now moving through the field,

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there is an induced upward current at both ends of the coil.

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Just as before, there is no induced current in the horizontal sections of the coil,

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and you can imagine that the two upward currents at the two ends cancel each other out,

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therefore no current flows around the coil. Of course, this also means that there is no

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induced EMF in the coil. Let's confirm this using Faraday's law.

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As we said earlier, there must be a change in the magnetic flux through the coil

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in order for an EMF to be induced. As the coil is moving inside the magnetic field,

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assuming that we have a uniform magnetic field, the number of field lines that enter the coil

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is the same as the number of field lines that leave the coil.

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As a result, the number of field lines inside the coil does not change,

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therefore the magnetic flux through the coil does not change.

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Since there is no change in magnetic flux, there is no induced EMF.

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Finally, let's see what happens as the coil is leaving the field,

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once again starting with Fleming's right hand rule.

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As the coil is leaving the field, the right end of the coil has already left the field,

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so here no current is induced, while since the left end of the coil is still moving in the field,

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here we have an induced current upwards.

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Once again, there is no induced current in the horizontal sections,

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so as the coil is leaving the field, there will be a clockwise current in the coil.

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Of course, as a result, there is also an induced EMF in the coil,

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which we can confirm by using Faraday's law.

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This time, the magnetic flux through the coil is decreasing,

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and since this is a change in magnetic flux, there will be an induced EMF in the coil.

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Examining the Faraday's law equation, we can also confirm that the sign of the induced EMF

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will be different when the coil is entering the field and when the coil is leaving the field.

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So for instance, if the induced EMF is taken to be positive when the coil is entering the field,

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it will be negative when the coil is leaving the field.

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This completes our discussion of induced EMF in a coil moving through a magnetic field.

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In the next video, we'll discuss what happens when a coil is turning in a magnetic field.