21.1 Physics 6B Magnetic Induction

21.1 Physics 6B Magnetic Induction - Physics6B...

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Physics 6B Magnetic Induction Prepared by Vince Zaccone For Campus Learning Assistance  Services at UCSB
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Before we can talk about induction we need to understand magnetic flux . You can think of flux as the number of field lines passing through an area. Here is the formula: Note that there are 3 parts to this formula: magnetic field strength, Area, and angle. We will learn that magnetic induction occurs if any of these change. In fact, the rate of change of flux is the induced voltage : Here is the formula: The negative sign helps to remind us of what induction does – induction always opposes the change in the flux. We call this Lenz’s Law. ) cos( A B flux B θ = Φ = t V B induced ∆Φ - = Next we will look at a few specific examples of a changing magnetic flux: Prepared by Vince Zaccone For Campus Learning Assistance  Services at UCSB
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1) A loop of wire entering a uniform magnetic field. X X X X X X X X X X X X X X X X X X X X X X X X v B Question: which direction is the induced current in the loop? Prepared by Vince Zaccone For Campus Learning Assistance  Services at UCSB
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1) A loop of wire entering a uniform magnetic field. X X X X X X X X X X X X X X X X X X X X X X X X v As the loop enters the B-field, the flux increases into the page, so there will be a current induced in the loop to oppose this increasing flux. The direction of the induced current is Counter-Clockwise, because that direction will create an induced B-field through the loop, out of the page (opposing the increase into the page). I induced B induced B Prepared by Vince Zaccone For Campus Learning Assistance  Services at UCSB
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1) A loop of wire entering a uniform magnetic field. X X X X X X X X X X X X X X X X X X X X X X X X v You might also notice that there will be a net force on the loop to the right, opposing its motion (try the right hand rule on each side of the loop). Induction opposes the change by trying to push the loop back out of the B-field. B I induced B induced Prepared by Vince Zaccone For Campus Learning Assistance  Services at UCSB
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X X X X X X X X X X X X X X X X X X X X X X X X 2) A loop of wire rotating in a uniform magnetic field. Question: which direction is the induced current in the loop? B Prepared by Vince Zaccone For Campus Learning Assistance  Services at UCSB
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X X X X X X X X X X X X X X X X X X X X X X X 2) A loop of wire rotating in a uniform magnetic field. As shown, the loop is intercepting the maximum flux. As it rotates, the flux will be decreasing, so there will be an induced current to oppose this change. The direction of the current will be clockwise, which creates an induced magnetic field through the loop, into the page. I induced
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21.1 Physics 6B Magnetic Induction - Physics6B...

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