Review Game

Field lines can never cross. If two field lines were to intersect, there would be two electric fields at the point of intersection, one associated with each line. However, there can only be one value of the electric field at a given point. 

The number of field lines that leave a positive charge or end on a negative charge is proportional to the magnitude of the charge. Since 8 lines leave the +4q charge, one-half of them (or 4) must end on the -2q charge, and one-fourth of them (or 2) must end on each of the -q charges.  

the field lines between the +4q charge and the -2q charge are parallel and evenly spaced, which would indicate that the field everywhere in this region has a constant magnitude and direction. 

Vertebrates and some invertebrates (like this lobster /crustacean) use the earth’s magnetic field to navigate and can determine its geographic location.

This ability may be related to the presence in the lobsters of the mineral magnetite, a magnetic material used for compass needles.