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Author Topic: how to find direction of induced current  (Read 7256 times)  Share 

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TyErd

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how to find direction of induced current
« on: November 09, 2010, 12:17:34 pm »
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how do you do it. I'm so confused
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Chavi

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Re: how to find direction of induced current
« Reply #1 on: November 09, 2010, 03:05:53 pm »
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Use Lenz's law. Simply find the direction of the current as you normally would (using the right hand slap tule - or curl rule) and then reverse the current to find induced current.

Remember that with Lenz's law, the induced current opposes the Change in Flux that preceded it. So there will only be a current if the field strength is changing. . . .
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TyErd

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Re: how to find direction of induced current
« Reply #2 on: November 09, 2010, 03:42:00 pm »
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how do you know the direction of the change in flux?
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Chavi

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Re: how to find direction of induced current
« Reply #3 on: November 09, 2010, 03:47:18 pm »
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Quote from: TyErd on November 09, 2010, 03:42:00 pm
how do you know the direction of the change in flux?
By the field lines. Do you have a specific question that you need answers?
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TyErd

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Re: how to find direction of induced current
« Reply #4 on: November 09, 2010, 03:51:29 pm »
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umm  question 10 2008 vcaa
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TyErd

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Re: how to find direction of induced current
« Reply #5 on: November 09, 2010, 03:55:28 pm »
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also question 14 of vcaa 07
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Linkage1992

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Re: how to find direction of induced current
« Reply #6 on: November 09, 2010, 03:55:50 pm »
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For that question, the external magnetic field is going into the page. As the coil is being removed, there is a loss of flux as it goes from an area where there is a magnetic field to one where there isn't.

To oppose this loss of flux, the induced current will produce a field which will go into the page through the centre of the coil. Using the right hand grip rule will show you that the current will have to go from Q to P.

An easy way to remember the direction of the induced field is: If it's being pulled out, the field will be in the same direction as the external field. If it's being put in, the field will be in the opposite direction.
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TyErd

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Re: how to find direction of induced current
« Reply #7 on: November 09, 2010, 04:04:02 pm »
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okay i get question 10 of vcaa 08 now, what about the 07  question?, coz nothing is being pulled out/in
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Re: how to find direction of induced current
« Reply #8 on: November 09, 2010, 04:21:09 pm »
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does increasing speed mean increasing magnitude of induced current? using more than one magnet increase magnitude of induced current?
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Re: how to find direction of induced current
« Reply #9 on: November 09, 2010, 04:34:29 pm »
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i dont get this question either. help?
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Chavi

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Re: how to find direction of induced current
« Reply #10 on: November 09, 2010, 04:43:37 pm »
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Quote from: TyErd on November 09, 2010, 04:34:29 pm
i dont get this question either. help?
Induced emf is the negative gradient of Flux.
Normally flux is modelled on a sine curve F=sin(t), so V= -d/dt (sint) = -cos(t).
With this, at M, the Flux through the coil should be zero (as voltage is at a maximum). So the figure is 9a
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fady_22

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Re: how to find direction of induced current
« Reply #11 on: November 09, 2010, 04:46:00 pm »
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9a.
Sketch the flux/time graph: it goes from 0 flux to max flux. You can see that at the point as shown in 9a, the rate of change of the flux is the greatest, hence the EMF would also be the greatest.

Edit: beaten.
« Last Edit: November 09, 2010, 04:52:49 pm by fady_22 »
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Chavi

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Re: how to find direction of induced current
« Reply #12 on: November 09, 2010, 04:50:38 pm »
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Quote from: fady_22 on November 09, 2010, 04:46:00 pm
9b.
Sketch the flux/time graph: it goes from 0 flux to max flux. You can see that at the point as shown in 9a (between 0 and max flux), the rate of change of the flux is the greatest, hence the EMF would also be the greatest.

Edit: beaten.
Why 9b? Max change in flux normally occurs when Flux =0 WB
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fady_22

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Re: how to find direction of induced current
« Reply #13 on: November 09, 2010, 04:52:25 pm »
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Quote from: Chavi on November 09, 2010, 04:50:38 pm
Quote from: fady_22 on November 09, 2010, 04:46:00 pm
9b.
Sketch the flux/time graph: it goes from 0 flux to max flux. You can see that at the point as shown in 9a (between 0 and max flux), the rate of change of the flux is the greatest, hence the EMF would also be the greatest.

Edit: beaten.
Why 9b? Max change in flux normally occurs when Flux =0 WB

You are correct.
Whoops. :P
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TyErd

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Re: how to find direction of induced current
« Reply #14 on: November 09, 2010, 05:01:48 pm »
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so when rate of change of flux is greatest(when flux=0), emf is also the highest? and that would also mean that when change in flux is minimum,(flux=max), emf is minimum?
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