Another example of motional emf is a rod attached at one end and rotating in a plane perpendicular to a uniform magnetic field. We can analyze this motional emf using Faraday’s law. 

(a) Consider the area that the rod sweeps out in each revolution and find the magnitude of the emf in terms of the angular frequency ω, the length of the rod R, and the magnitude of the uniform magnetic field B. 

(b) Write the emf magnitude in terms of the speed v of the tip of the rod and compare this with motional emf magnitude of a rod moving at constant velocity perpendicular to a uniform magnetic field.