A charge of -0.30C is placed on a circular conducting plate (very thin) with radius R= 10 cm. a) Draw a diagram of the situation described above, and calculate the surface charge density a. b) What is the magnitude of the electric field at a point 3.0 cm above the center of the plate? e) What is the magnitude of the electric field at that point if a 5 cm hole is placed in the center of the disk. Hint: This is a tricky one. Use the principle of superposition: this is equivalent to having a Sem radius disk of equal POSITIVE charge in the middle of your disk of negutive charge, so that the charges cancel.