# Electricity and magnetism (magnitude of magnetic field)

1. Jun 27, 2012

### 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?

2. Jun 27, 2012

### 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?

3. Jun 27, 2012

### swankymotor16

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

4. Jun 27, 2012

### 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?

5. Jun 27, 2012

### 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?

6. Jun 27, 2012

### Simon Bridge

7. Jun 27, 2012

### swankymotor16

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

8. Jun 27, 2012

### 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.