DP 3.1 (50 points) A uniform electric field exists between two sufficiently large*, conducting plates separated by 1.2 mm. A dust grain with charge 50 nC, located between these two plates, feels a 20-N electric force. (a) Find the magnitude of the electric field between these two plates. (b) Calculate the potential difference between these two plates. *Remark: When the two conducting plates are sufficiently large, it implies that the electric field between the two plates is uniform. In this case, the distance between the two plates is much smaller than the dimension of each plate. (We don't need to know the dimension of each plate for this problem.) DP 3.2 (50 points) In this figure, it is known that charge 4. =+10.0 JC , charge 9, = -10.0 HC, charge 4- =+15.0 JC and charge q, = -15.0 JC. And the locations of these four point charges have been specified in this figure. x = -2.00 cm x = +5.00 cm Calculate the total electric potential at the O origin O due to these four point charges. 9 B Remark: When you consider V = k - due -y= -2.00 cm qc to each point charge, please keep in mind that each distance r, should be a positive quantity. 9 p y= -3.00 cm