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a. Show that the magnetic dipole moment of a ring of radius r holding a charge 4 evenly distributed round the ring which is rotating at angular velocity w is given by 1 H=2qwr b. A disc of radius R holds a charge Qevenly distributed across the surface. This disc is rotating at angular velocity was shown below. z 0 R Ota Q By considering this disc as a concentric series of rings, show that the strength of the magnetic dipole moment of the rotating disc is given by c. Consider a small ring of radius a located a distance z>rand R from the axis of the disc as shown above. Calculate the magnetic flux through this ring. You may use that the magnetic field from a magnetic dipole ji is given by 21 23 for large d. If the rotating disc is now accelerated with angular acceleration a, then, (i) Calculate an expression for the induced emf round the ring. (ii) With the aid of a diagram determine the direction of the force: justify your answer and discuss the physical laws involved