stuck on light intensity problem.... 1. The problem statement, all variables and given/known data http://s685.photobucket.com/albums/...ew¤t=physicsexam2q5withoutphotocell.jpg A conducting rod slides down 2 frictionless copper tracks at a constant velocity. There is a .50 T magnetic field perpendicular to the rod. The rod maintains electrical contact at all times. The rod has a length of 1.0 m and a mass of .25kg. A 1.5 Ohm light bulb is attached between the tops of the tracks. What is the intensity of the light from the light bulb at a distance 3.0 away from the bulb? 2. Relevant equations S = c / (magnetic permeability of free space) * B^2 3. The attempt at a solution S = ? B = .50 c = 3.00 *10^8 m/s (magnetic permeability of free space) is a constant... = 4pi *10^-7 T*m/a if all these variables are plugged into the equation i can solve for S and get the intensity. But "3 meters" is mentioned in the problem. I know im using the wrong formula...which one am i supposed to use?