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

[McAfee]

Homework Statement

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.

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?

 

[vela]

Homework Statement

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.

The Attempt at a Solution

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

In what way?

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?

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

 

[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?

 

[vela]

Yes, that's right.

 

[asteriatic]

Your reasoning is correct. When the magnetic field is perpendicular to the section's area vector, the angle between them is 90 degrees and therefore, the dot product of the two vectors is zero. This means that there is no magnetic flux passing through the section of the closed surface, resulting in a magnetic flux of zero. This can also be explained using Faraday's Law, which states that the induced electromotive force (EMF) is equal to the rate of change of magnetic flux. Since there is no magnetic flux, there will be no induced EMF, leading to a magnetic flux of zero.