Charge q is uniformly distributed on a disk of radius a. (a) evaluate o in terms of q and a. (uniform means not a function of position-variable r! ) (b) evaluate the enclosed charge function q(r) for 0 srce in terms of r and the constants q and ar; graph this function for 0 sr . always check solutions at the limits of a variable's range. here q(r=0) = 0: qr 2 a) = q. charge may lie in points q, or be distributed on lines, on surface sheets, or in volumes, with densities: charge-per-unit-length a = dy/dl; charge-per-unit-area o = dq/da ; or charge-per-unit-volume p = dp/dr. these distributions can be squeezed or stretched into one another, involving mathematical infinities.