Question 7 (a) An innite sheet carries a uniform surface charge density 0 > 0. Consider the point P at a distance r above the sheet. By what factor would the electric eld at point P get weaker if a circular section with radius r was removed from the sheet, beneath point P? (b) Consider a thin, uniformly charged spherical shell with radius r, carrying a positive charge of Q. A small hole is created, removing 0.02% of the shell, so that a measurement probe can be inserted. What will the measured magnitude and direction of the field be at the centre of the shell