Magnetic flux a scalar or vector?

[almostatrap]

This is bugging me.

So flux is a scalar quantity, why should if ever be negative, like in graphs with rotating coils?

If Φ = BA⊥ = BAcosθ where where θ is the angle between the field and the normal to the coil. So if the coil rotates 180 degrees, isn't the angle just 0?

What does vcaa want, anyway?

[NE2000]

Always thought flux was a vector quantity....was I just mistaken?

[kamil9876]

flux can be positive or negative. In most contexts flux is defined as fields strength.area vector. Area vector is a vector. Also negative flux is a good concept to have when it comes to faraday's law since it coincides so well with negative emf.

[TrueTears]

Since 'B' is a vector and it's 'multiplied' by a scalar A, then flux must be a vector.

[almostatrap]

cool. thanks!

[bigtick]

Magnetic flux is defined as the dot product of B and A, so it is a scalar.

[kamil9876]

bigtick is correct. Note however that flux can still be negative or positive. The phrase "vectors are positive and negative and scalars are positive" is in fact incorrect. Vectors have direction, more than just in the positive or negative x axis but in all sorts of directions and dimensions. Scalars on the other hand can be (vaguelly) described as things you can multiply a vector by to "scale" the vector (negative scalar meaning you can reverse the direction).

As to the "area vector", in more formal treatments of flux it is the vector pointing perpendicular to the surface with the same area, hence the magnitude of the flux is simply BA when the magnetic field is parralel to area vector(hence perpendicular to surface).