b) What is the resonance frequency of a 4mH coil connected in series with a 9μF capacitor? c) How fast is a proton moving if it is to follow a circular path with a radius of 2.0 cm in a perpendicular magnetic field of 0.9×10−4 T ? 4. a) A 120 V,180/πHz power source is connected across a 4H inductor. How large is the current drawn from the source if the resistance of the coil is negligible? b) Assume that the heaters of a vacuum tube require a voltage of 24 volts. What should be the ratio of primary to secondary turns on a transformer that is used to operate the tube from a 480 V line voltage?