Solved: A search coil for measuring B (also called a flip

Chapter , Problem 68

(choose chapter or problem)

A search coil for measuring B (also called a flip coil) is asmall coil with N turns, each of cross-sectional area A. It isconnected to a so-called ballistic galvanometer, which is adevice to measure the total charge Q that passes through itin a short time. The flip coil is placed in the magnetic field tobe measured with its face perpendicular to the field. It isthen quickly rotated 180 about a diameter. Show thatthe total charge Q that flows in the induced current duringthis short flip time is proportional to the magnetic field B.In particular, show that B is given byB =QR2NAwhere R is the total resistance of the circuit, including thatof the coil and that of the ballistic galvanometer whichmeasures the charge Q.