Figure 17.51 shows some of the elec- tric field lines due to three point charges arranged along the vertical axis. All three charges have the same magnitude. (a) What are the signs of the three charges? Explain your reasoning. (b) At what point(s) is the magnitude of the electric field the smallest? Explain your reason- ing. Explain how the fields produced by each individual point charge combine to give a smal net field at this point or points. (a) A closed surface encloses a net charge of 2.50