An example of magnetohydrodynamics (mhd) comes from the flow of a river (salty water). this fluid interacts with the earth’s magnetic field to produce a potential difference between the two river banks. how would you go about calculating the potential difference?

Light from two different sources are incident upon the same side of a polarizing filter. light from one source is polarized with total intensity ip, while light from the other source is unpolarized with total intensity iu. as you rotate the polarizing filter through 360 degrees, the intensity of the transmitted light on the other side varies by a factor of 9. what is the relative intensity of the initial polarized source to the unpolarized source, or ip/iu?