(a) The electric field on the surface of a thin spherical shell of radius 0.5 m is measured to be 800 N/C and points radially towards the centre of the sphere. What is the net charge within the sphere's surface? (b) An electric field of 120 N/C points down over a football field. Calculate the surface charge density on the field. (c) What would be the total electric flux if the field is 100x75 m2 .