Hey, where are the Magnetic fields?.. That's for me to know and for you to find out! In the lower right corner, there is a wire (think of it sticking into and out of the screen). In the other three corners, there are magnetic fields of specific directions and magnitudes. Assume that the magnetic fields are constant in their own quadrants, and act in the plane of the screen. Click on the wire, and drag it into the other three quadrants .. you will see a Force vector show up (and the value of the force is indicated  notice that it is N/m .. that is Force/length for the wire). If you assume that the current is going into the screen (with a current magnitude of 1.5 A), can you figure out the strength of the magnetic field, and the direction? You should be able to figure out the directions just by knowing the current direction and the resultant force directions, but if you really must cheat (or if you want to check your answers), you could turn on the magnetic field vectors below. [Note that the field vectors are showing the results of the wire's magnetic field as well as the fields in each of the quadrants (a vector sum).] 

Credits Original Physlet problem authored by Mario Belloni. Modified by Scott Schneider