Electricity and magnetism (magnitude of magnetic field)

[swankymotor16]

A 1000-turn toroidal solenoid has a central radius of 4.2 cm and is carrying a current of 1.7 A. What is the magnitude of the magnetic field inside the solenoid at the central radius? (μ0=4∏×10^-7 T ∙ m/A) r= 4.2cm= 0.042m

B=(μ0)(I)/(2∏)(r) ⇔ (4∏×10^-7)(1.7)/(2∏)(0.042) ⇔ 1.43x10^-8 T? Or does the 1000-turn toroidal affects in the magnetic field in some sort of a way?

 

[Simon Bridge]

Would you expect a long coil of wire to have a different field to a single loop?
What would you expect for the field due to two loops of current?

 

[swankymotor16]

yes. But, how different will be? Is there a formula for it?

 

[Simon Bridge]

Don't go by formulas, use your understanding of how magnetic fields work - if one loop had a field of B, and you added another one the same, what do you think would happen to the field?

 

[swankymotor16]

that's the problem! I don't know how magnetic fields work! I have a bad teacher, and I'm running out of time! Another source told me that there's no current in the center, and by Ampere's Law the current in the center is zero. is this true?

 

[Simon Bridge]

OK - magnetic fields add together, so each loop add another B to the total field in the center.

Lots of people find the hyperphysics pages top them up quickly where their classes are lacking. eg: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html ...

 

[swankymotor16]

that's great! I was missing the N, the 1000 turns. thank you!

 

[Simon Bridge]

That's cool ... the lesson here is that electric and magnetic fields add together. This is called "the superposition principle". Make sure you work through the hyperphysics pages to bring you up to speed.