A non-conducting, uniformly charged disc of surface charge density o, radius R and negligible thickness is rotating about its axis with an angular velocity w. (a) Consider a thin circular loop of radius dr at a distance r from the disk center as shown on the picture. Show that the charge on the thin loop is given by dq=2.7or dr. (b) What is the magnetic field dB at the center of the disc, created by the rotating charge dg calculated in (a)? Hint: what is the current dI due to the rotation? (c) Calculate the total magnetic field B at the center of the disc. (d) What is the direction of B?

A non-conducting, uniformly charged disc of surface charge density o, radius R and negligible thickness is rotating about its axis with an angular velocity w. (a) Consider a thin circular loop of radius dr at a distance r from the disk center as shown on the picture. Show that the charge on the thin loop is given by dq=2.7or dr. (b) What is the magnetic field dB at the center of the disc, created by the rotating charge dg calculated in (a)? Hint: what is the current dI due to the rotation? (c) Calculate the total magnetic field B at the center of the disc. (d) What is the direction of B?