Figure 18.67 below represents the electric field in the vicinity of three small charged objects, R, S, and T. The objects have charges −q, +2q, and −q, respectively, and are located on the xaxis at −d, 0, and d. Field vectors of very large magnitude are omitted for clarity.

 Briefly describe the characteristics of the field diagram that indicate that the sign of the charges of objects R and T is negative and that the sign of the charge of object S is positive.
 Briefly describe the characteristics of the field diagram that indicate that the magnitudes of the charges of objects R and T are equal and that the magnitude of the charge of object S is about twice that of objects R and T.
For the following parts, an electric field directed to the right is defined to be positive.
 On the axes below in Figure 18.68, sketch a graph of the electric field E along the xaxis as a function of position x.
 Write an expression for the electric field E along the xaxis as a function of position x in the region between objects S and T in terms of q, d, and fundamental constants, as appropriate.
 Your classmate tells you there is a point between S and T where the electric field is zero. Determine whether this statement is true, and explain your reasoning using two of the representations from parts (a), (b), or (c).