Which field Passes Through the Polarization Film? Why Isn’t the Perpendicular Field Stopped? When one EM field is aligned so that it can pass through a polarizing lens the other field (E or B) is 90 degrees out. Is only one of the EM fields affected by a polarizing lens or film? How is it that one field is stopped yet the other seems unaffected?
 A: One way of making a polarizing film is having a lot of small narrow conducting 'rods' inside it. The rods are much longer than they are wide, and are mostly oriented in the same direction. The spacing between the rods is on the order of the wavelength of light. Imagine, for lack of a better analogy, the bars on a prison cell.
When light enters the polarizing film, the mode with electric field oriented along the direction of the rods excites the electrons inside the rods and vibrates them, in much the same way as happens in an antenna. Thus the light interferes with itself and cancels out.
The mode with electric field oriented perpendicular to the direction of the rods is not able to excite the electrons inside very well, as they are restricted to only moving in a very small length (the width of the rods). Thus that mode is unaffected and passes through.
This is a very very simplified picture and there's lots of other ways to polarize light without the use of conducting material at all. But it's useful to get a general idea of what happens.
A: Both fields are equally affected by the polarizing rods/wires, it is just more conventional to visualize a small wire as being directly interfering with the E-field that is parallel with it than the B-field that is perpendicular to it. 
You would never ask this question if had been taught to view the B-field not as a vector field but instead what it really is a bi-vector or an anti-symmetric tensor, which is a bit of a mouthful. In some more advanced texts you would be told the B is not really a vector but instead it is a pseudo- or axial-vector and its properties are similar to torque that is the vector product of two (true) vectors. 
In any case, when viewed as such the bi-vector field is actually parallel with the wire, and its source is the current. The bi-vector field itself is a set of surfaces emanating/ending in the current carrying wire. The conventional vector B-field consist of the orthogonal rays to these bi-vector surfaces.
If you do not care about all that stuff then just recall that an infinite long wire generates a magnetic "vector" field that are in circles perpendicular to the wire and therefore those polarizing rods that are parallel with the E-field will also block the B "vectors" perpendicular to it.
