An 
-particle and a proton are at rest a distance 
apart in a vacuum, as illustrated in the figure below.
A point P is distance 
from the -particle along the line joining the -particle to the proton as shown in the figure above. The variation with distance of the electric field strength 
due to the -particle alone is shown in the graph below.
The variation with distance of the electric field strength 
due to the proton alone is also shown in the graph above. Explain why the two separate electric fields have opposite signs.
