# When is the magnetic flux on a section of a closed surface equal to zero?

1. Apr 6, 2012

### McAfee

1. The problem statement, all variables and given/known data

When is the magnetic flux on a section of a closed surface equal to zero?

A. When the magnetic field is in the direction opposite that of the section’s area vector.
B. When the magnetic field is in the direction of the section’s area vector.
C. When the magnetic field is perpendicular to the section’s area vector.

3. The attempt at a solution

I have ruled out the answer A because it doesn't make sense.

I think it is C because when perpendicular it might cancel out it out. I'm not sure whether you have to use Lenz's or Faraday's Law?

2. Apr 6, 2012

### vela

Staff Emeritus
In what way?

You're simply being asked to find the flux. You don't need to use either law.

3. Apr 6, 2012

### McAfee

Oh. ok so flux = B.A.cos x , where x is the angle between magnetic field and area vector.
since x= 90 degree cos x = 0 and hence flux = 0.

The answer is C. I'm a right?

4. Apr 6, 2012

### vela

Staff Emeritus
Yes, that's right.