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Edexcel Jan 2007 unit 5 help

Hi all

I just cannot do this phys question. I am attaching a file. Pls suggest ?
-6735 (01) - Physics.pdf17.2KB
Reply 1
Avatar for Eau
Eau
15
Haven't done the paper yet, please let me do it first, and then I will help you! Be patient :smile:!
Reply 2
Avatar for Eau
Eau
15
Use Right-Hand Grip rule: http://www.gcse.com/energy/em4.htm
Reply 3
Avatar for Mohit_C
Mohit_C
10
Simply the R-H rule. The 8A has an anti-clockwise magnetic field and so does the 2A (as they both travel in the same direction). Therefore midway between the wires, the 8A's magnetic field goes into the paper and the 2A goes out of the paper. You can see that there should be a decrease in the magnetic field as there's an interaction. This is exactly what they ask you in the second question. You have to use B=(u0)I/2pir where u0 is the permeability of free space, r is 1.5cm and you calculate both magnetic field. Now you know that the 8A has a larger magnetic field (as current is proportional to the magnetic field). Therefore the resultant field goes into the paper and its value is (magnetic field caused by 8A)-(magnetic field caused by 2A).
Reply 4
Avatar for shuvo89
shuvo89
OP
thanks a lot Mohit. For some weird reason i didn't look at the current in both wires.
Reply 5
Avatar for fabbo
fabbo
I always thought with these questions, the force actig on each wire is caused by the magnetic flux density of the other wire. Therefore the magnetic field of the 2A wire would be greater than that of the 8A - but its the other way round - why?
Mohit_C
Simply the R-H rule. The 8A has an anti-clockwise magnetic field and so does the 2A (as they both travel in the same direction). Therefore midway between the wires, the 8A's magnetic field goes into the paper and the 2A goes out of the paper.


Why is it midway through the wires, the 8A's magnectic field goes into the paper and the 2A goes out.
Reply 7
Avatar for Mohit_C
Mohit_C
10
Goodfella1989 that's what the question asks you to calculate.
It doesnt actually state that the 8As magnectic field goes into the paper and that the 2A goes out. I mean how did you come to that assumption?
Reply 9
Avatar for Darxy
Darxy
Corkscrew rule :smile: imagine looking at the end of the wire so the current is going away from you, and apply the corkscrew rule - look it up if your not familiar with the rule! :smile:
Reply 10
Avatar for Mohit_C
Mohit_C
10
Goodfella1989
It doesnt actually state that the 8As magnectic field goes into the paper and that the 2A goes out. I mean how did you come to that assumption?


I misunderstood you then. Darxy is right, simply corkscrew rule. If thumb is upwards, magnetic field is anti-clockwise, and vice versa.
ok thanks

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