For all problems, please show explicitly the work that you have done to arrive at your answer. It is helpful to note the property you have used to arrive at your answer, and to include such equation before inserting numerical values. Remember to include units & to mind your significant figures! You may find it helpful to draw a diagram, but this is not required.

4. Calculate the electric field at the upper right point in Fig. 2. The charges are fixed in place, the square lattice has length a. +20 Fig. 2. Fixed charge distribution on square lattice of length a. 5. A test charge is placed at the upper right point in Fig. 2., what is the magnitude of the electric force on the test charge due to the fixed charges of problem 4