where the hell does the k come from? (1 Viewer)

[Inhuman]

OK I now know thanks to reading my texktbook that F=kI/d but where the hell do they get 2.0 x 10^-7 from? It seems like just a random number pulled out of the air, and it's not on the data sheet or anything

 

[Chand]

its on the data sheet..abt halfway down...magnetic force constant

 

[Bannanafish]

it's a constant

 

[helper]

Wrong equation

F/l =kI1I2/d

k=magnetic force constant (on data sheet)

 

[inasero]

uh mate u got the formula wrong...its

F/l=(kIoneItwo)/d

and im pretty sure that the constant is in the data sheet...otherwise it wont hurt ur brain too much to remember the number

 

[Inhuman]

Ah thanks for pointing out my blindness Chand; now I won't have to memorize some meaningless variable for tomorrow

and for those pointing out my 'wrong' equation, I know it's not the official one but it comes in handy for certain problems. Thanks anyway

 

[ghoolz]

Yeah k is on the data sheet. Its the 8th value down, its called magnetic force constant.

Not sue how they get it one said that it was "derived from careful experimentation" and another didnt say anything.

Note: that the formula is actually F= k(I I)/d

there are two I's onr for each current carrying conductor

 

[ghoolz]

there were a lot of quick posts then, there was nothing when i started to write and then check two textbooks and then suddenly there were heaps

 

[Constip8edSkunk]

Originally posted by Inhuman
and for those pointing out my 'wrong' equation, I know it's not the official one but it comes in handy for certain problems. Thanks anyway

actually its B=kI/d. you get the F/l equation by substituting B with F/Il (as F=BIl, @=pi/2 here)

 

[helper]

Inhuman, you write that equation in an exam and it will be marked wrong.

It is either Amperes law for force, as most people posted, or the magnetics field strength as posted by constipated. The one you wrote is meaningless.

 

[Inhuman]

OK OK I realise my mistake. The offending equation shall be erased from my memory

 

[Chand]

Originally posted by Inhuman
Ah thanks for pointing out my blindness Chand;

No problem. Good luck for tommorrow.

 

[MyLuv]

B=kI/d for a straight Conducting wire
wat about a circular wire???Ive seen it some where but cant remember now,do we need it??

 

[ghoolz]

Not sure if they would ask a circular wire. I dont think I've seen a question like that. They can fold it into a square/rectangle and ask about that and then place that near one or two magnets, to make a motor

 

[wogboy]

Don't worry about calculating magnetic fields for irregularly shaped wires (e.g. circular), it's not in the HSC.

If you wanted to calculate the magnetic field in a circular wire loop, you need to use a formula called the Biot Savart Law, which in essence is the process of splitting the curved wire into many infinitely small lengths of straight wire, and integrating the contribution of each of these straight lengths. Again, you don't need to know this.

 

[Rahul]

Originally posted by wogboy
If you wanted to calculate the magnetic field in a circular wire loop, you need to use a formula called the Biot Savart Law, which in essence is the process of splitting the curved wire into many infinitely small lengths of straight wire, and integrating the contribution of each of these straight lengths. Again, you don't need to know this.

sounds like you would have to initially differeniate the curve(circular wire) and find the gradient of it....hence the straight lines. and then working out the magnetic field for each of these infinitely small lines and then intergrating it back to the function. close?