HOW do u do this MC for Physics? (1 Viewer)

[orcevalm]

hey guys for some reason i can't get the answer to this MC if someone helps that would be much appreciated
Thanks in advance!

 

[seventhroot]

Look at the formula for B, take the ratio and you will find that the answer is A

 

[orcevalm]

Look at the formula for B, take the ratio and you will find that the answer is A

the answer is c

 

[mreditor16]

Look at the formula for B, take the ratio and you will find that the answer is A

the answer is c

lol'd so hard.

 

[itsalberttrinh]

Using B = kI/d we can calculate that the magnitude of the magnetic field strength at both P and Q (5x10^-6). Substituting into option A and B is untrue, so I would rule them out. That leaves option C and D, it makes sense that the further we move away from the wire, the weaker the magnetic fields are so D would not be correct and C would be the answer.
Also its you can just simply see that at a distance of 10cm, the magnetic field strength is B and at a distance of 5cm the magnetic field is 2B. Thus C would be the best answer as options A and B are no true for all cases.

 

[orcevalm]

Using B = kI/d we can calculate that the magnitude of the magnetic field strength at both P and Q (5x10^-6). Substituting into option A and B is untrue, so I would rule them out. That leaves option C and D, it makes sense that the further we move away from the wire, the weaker the magnetic fields are so D would not be correct and C would be the answer.
Also its you can just simply see that at a distance of 10cm, the magnetic field strength is B and at a distance of 5cm the magnetic field is 2B. Thus C would be the best answer as options A and B are no true for all cases.

oh right that makes sense thanks!

 

[mlpd]

You re welcome bro


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[anomalousdecay]

The answer is C.

I did it using Ampere's Law, (the proper method involves integration actually and it makes more sense but I won't go through in detail here unless someone wants it in particular) and actually found the proper relationship for the magnetic field due to a current carrying conductor.

In fact, looking online the HSC expression of Ampere's Law (really, really misleading as the expression for Ampere's Law is a bit more complex and thorough actually) is:



Using that, you can see that the answer is C clearly. For keen students (note that none of the below is in HSC and no-one has to know this for HSC):

Spoiler

Really, Ampere's Law is thoroughly stated as an integral of B.ds = 2*pi*k*I , where I is the current enclosed within the Amperian loop. For HSC intents and purposes this is not necessary, but for those curious students out there this allows you to calculate the magnetic field produced by many other shapes of wire, including toroids, loops, solenoids and many other odd shapes which can be simplified and the resulting magnetic field produced can be found as a function of distance from the wire. Interestingly you can even obtain it so that the magnetic field is dependent on the inverse of the logarithm of the distance from the wire.