# Help with confusing magnetic fields question?

#1
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
0
7 years ago
#2
Sorry, but your thumbnail is readable. Could you tell me what the problem is? or give a better attachment at least?
0
#3
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'.
0
7 years ago
#4
Use Emf = flux/time (the gradient) and you should be able to get it from there
1
7 years ago
#5
(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?
1
#6
(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

(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?
0
7 years ago
#7
(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.
1
7 years ago
#8
(Original post by itsallokay)
Thanks and that makes sense

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?
0
#9
(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
0
7 years ago
#10
(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?
0
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