Aparallel-plate capacitor has circular plates of radius that are separated by a distance In the gap between the two plates is a thin straight wire of resistance that connects the centers of the two plates. A time-varying voltage given by is applied across the plates. (a) What is the current drawn by the capacitor? (b) What is the magnetic field as a function of the radial distance from the centerline within the capacitor plates? (c) What is the phase angle between the current drawn by the capacitor and the applied voltage?
38. Two electrons move in opposite directions at 0.70c as measured in the laboratory. The speed of one electron as measured from the other is: A. 0.35c B. 0.70c C. 0.94c D. 1.00c E. 1.40c ans: C 39. Light from some stars shows an apparent change in frequency because of: A. interference B. refraction by layers of air C. diﬀraction D. reﬂection E. relative motion ans: E 40. While emitting light of proper frequency f 0, a source moves to the right with speed c/4 relative to reference frame S. A detector, to the left of the source, measures the frequency to be f, which is greater than f 0 . This means: