# Magnetic fields and current

1. Aug 11, 2009

### Maxwellkid

I'm trying to find out which logical statement is true.

If and only if there is a region of space where there is no current, there cannot be a magnetic field that is both unidirectional and nonuniform.

Or

if there is a region of space where there is no current, there cannot be a magnetic field that is both unidirectional and nonuniform.

Which statement is true????

2. Aug 11, 2009

### Staff: Mentor

What is the context for the question? Is it for schoolwork?

What are the relevant equations for figuring this out? There are a couple of equations that relate current and magnetic field...

3. Aug 11, 2009

### Red_CCF

aren't these two statements exactly the same?

4. Aug 11, 2009

### Maxwellkid

no, first statement is an equal sign. if and only if x then 5 means x=5

second statement is an if and then statement. if x then 5 doesnt mean x=5 because if 5 then x cannot be concluded.

2 statements are NOT logical the same.

5. Aug 11, 2009

### Staff: Mentor

6. Aug 11, 2009

### Maxwellkid

i'm using Ampere's law to investigate nonuniform unidirectional B fields.

7. Aug 11, 2009

### Staff: Mentor

Cool. So can you show us how to use Ampere's Law to start go answer your questions?

8. Aug 11, 2009

### Maxwellkid

i would draw a rectangular dL with 2 sides of the rectangle parallel and antiparallel to nonuniform and unidirectional B field lines.

$$\oint \vec{B}\cdot \vec{dL} = \mu_{o} I_{enc}$$

where $$I_{enc} = 0$$