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Help with confusing magnetic fields question?

Hi guys,

I just needed help with the following question. The answer is C but i don't understand how. Any help will be much appreciated.

Thanks
20150131_210918.jpg512.9KB
Sorry, but your thumbnail is readable. Could you tell me what the problem is? or give a better attachment at least?
Reply 2
Avatar for itsallokay
itsallokay
OP
1
it is the graph one

it says
'The magnetic flux through a coil varies with time as shown by the first graph. Which one of the following graphs, A to D best represents how the magnitude of the induced emf varies in this same period of time'.
Reply 3
Avatar for JamGrip
JamGrip
1
Use Emf = flux/time (the gradient) and you should be able to get it from there
(edited 9 years ago)
Reply 4
Avatar for MSB47
MSB47
2
Original post by itsallokay
Hi guys,

I just needed help with the following question. The answer is C but i don't understand how. Any help will be much appreciated.

Thanks


Induced EMF is equal to the rate of change of magnetic flux linkage (Faradays law) so when the graph of flux against time shows a region where it is a straight line, there is no induced emf because it is not changing moreover, when the magnetic flux is decreasing and shows a downward diagonal line there is a rate of change of magnetic flux and therefore there is a constant value of induced emf. Following that basic idea should help you realize that it is C. By the way are you doing AQA?
Reply 5
Avatar for itsallokay
itsallokay
OP
1
Original post by JamGrip
Use Emf = flux/time (the gradient) and you should be able to get it from there


Thanks and that makes sense :smile:

Original post by MSB47
Induced EMF is equal to the rate of change of magnetic flux linkage (Faradays law) so when the graph of flux against time shows a region where it is a straight line, there is no induced emf because it is not changing moreover, when the magnetic flux is decreasing and shows a downward diagonal line there is a rate of change of magnetic flux and therefore there is a constant value of induced emf. Following that basic idea should help you realize that it is C. By the way are you doing AQA?


Thanks and yes AQA. And what year and subjects are you doing?
Original post by itsallokay
it is the graph one

it says
'The magnetic flux through a coil varies with time as shown by the first graph. Which one of the following graphs, A to D best represents how the magnitude of the induced emf varies in this same period of time'.


JamGrip's formula put it in a nutshell: the induced electromagnetic field depends on the flux at the time. The flux is changing by the changing time. If the first graph shows the flux, you can see that its at a maximum first (straight line), before the flux decreased (downward line). After that the flux is increased to a certain moment and keeps a constant value which is below the maximum (another straight line).

As the electromagnetic field is connect to the flux, it is adapted. That is why the highest straigt line of the electromagnetic field is at the maximum of the flux and the decreased one of the electromagnetic field is at the decreased flux line. So C fits at best.
(edited 9 years ago)
Reply 7
Avatar for MSB47
MSB47
2
Original post by itsallokay
Thanks and that makes sense :smile:



Thanks and yes AQA. And what year and subjects are you doing?


im in second year doing physics maths and politics, finding physics this year extremly challenging how about you?
Reply 8
Avatar for itsallokay
itsallokay
OP
1
Original post by MSB47
im in second year doing physics maths and politics, finding physics this year extremly challenging how about you?


I'm also in second year doing Chemistry, Biology, Physics and Maths and agree that physics is kinda tough
Reply 9
Avatar for MSB47
MSB47
2
Original post by itsallokay
I'm also in second year doing Chemistry, Biology, Physics and Maths and agree that physics is kinda tough


you planning to go uni next year?

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