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This video is about induced electromotive force or induced EMF.

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We'll start by learning high current is induced and then move on to discuss

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how to use Fleming's right hand rule for induction effects.

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Let's see high current is induced. Recall from subtopic 5.4 that when charge moves in a magnetic

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field it experiences a force due to the field. The idea of an induced current is closely related

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to this concept. Induced current is defined as the production of a current in a conductor

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due to a relative change between the conductor and the magnetic field. By relative change we

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often mean relative motion, so for example a conductor that moves in a magnetic field.

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Other examples of changes are changes in magnetic field strength or magnetic field direction.

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Later in this subtopic we'll learn about magnetic flux and magnetic flux density.

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Both of these quantities are connected to induced current and induced EMF.

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Next let's see an example of how induced current is produced. Let's assume that we have a magnetic

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field that is pointing out of the page or screen. A conducting metal rod is moving in this magnetic

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field horizontally to the right. The rod is moving at a constant speed. Let's apply Fleming's left

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hand rule that we learned in subtopic 5.4. The rod contains positively and negatively charged

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particles. For now let's focus on what happens to a positively charged particle

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as the rod moves through the magnetic field. Since the positive charge together with the rod

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is moving to the right, the direction of the conventional current is to the right,

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so when we are using Fleming's left hand rule our middle finger should be pointing to the right.

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The field direction is out of the page or screen, so our index finger should be pointing out of the

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page. If you got the direction of these two fingers correctly, you will see that your thumb

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is pointing downwards. Therefore the force due to the field that acts on the positive charge

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is pointing downwards. Since the direction of the electromagnetic force that acts on a positive

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charge is downwards, the direction of the electromagnetic force that acts on negative

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charge is upwards. As a result electrons in the rod flow upwards, so the direction of the

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conventional current is downwards. The current that is produced in the rod this way is called

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induced current. It is induced by the relative change between the rod and the magnetic field.

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You might be wondering how can there be a current in the rod when it is just a piece of metal and

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it is not part of a closed circuit. An important concept here is that a current is induced in the

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rod even though the rod is not part of a closed circuit. What eventually would happen is that

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negative charge would accumulate at one end of the rod while positive charge would accumulate

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at the other end. As a result after some time charge would stop moving. So in order to induce a

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continuous current, the conductor must be part of a closed loop. Of course when the current is

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induced electrons gain energy, so energy transfer takes place. Some form of energy is transferred

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into the electrical energy of the electrons. Since energy is transferred into electrical

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energy, we say that an EMF or Electromotive Force is induced in the conductor. Keep in mind that in

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spite of what its name suggests, Electromotive Force is not a force but it is the electrical

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energy per unit charge that is transferred to the electrons and it is measured in volts.

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Through our example of the moving rod, we have seen how Fleming's left hand rule can be used

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to find the direction of the induced current. Fleming also has a right hand rule that can

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be used in this situation to determine the direction of the induced current. Let's see how this rule

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works. Logically for this rule we'll use our right hand. Our thumb will point in the direction of

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the conductor's motion. Our index finger in the direction of the magnetic field and our middle

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finger will show the direction of the induced conventional current. Let's go back to the

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moving rod in the magnetic field from our previous example and use Fleming's right hand rule to find

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the direction of the induced conventional current. Position your right hand so that your thumb is

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pointing in the direction of the conductor's motion so to the right your index finger should

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point in the field direction so out of the page or screen and if you have done this correctly

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your middle finger should point downwards showing you the direction of the induced conventional

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current. This is the same direction that we found using Fleming's left hand rule in the previous video.

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So when you work with the induced current you can use either of these rules to work out directions.

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Let's summarize what we have learned in this video. We began by discussing induced current

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and defined the meaning of this term. Then we examined a metal rod moving through a magnetic field

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and explained step by step how a current is induced in the rod. We added that during the

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induction process energy transfer takes place so we say that an EMF is induced in the conductor.

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In the second part of the video we learned about Fleming's right hand rule

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which we can use to find the direction of the induced current. When using this rule we should

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point our thumb in the direction of the conductor's motion align our index finger with the field

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direction and if we do this correctly our middle finger will show the direction of the induced

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conventional current. We concluded that when working with induced current we can use either

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Fleming's left hand or right hand rule. This completes our discussion of induced

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electromotive force or induced EMF. In the next video we'll learn about Lentz's law.