Components of magnetic field

 We did this experiment to measure components of magnetic flux density B. There was a.c. in the large copper coil which created a rapidly alternating magnetic flux. There was thus a large enough rate of change of flux density in the small yellow search coil to induce an alternating emf. We varied the angle of the search coil so that it was detecting different components of the flux. The largest flux is detected in the position shown below.

We displayed the induced emf on an oscilloscope and measured the peak-to-peak voltage, halving it to read the peak emf. This procedure reduces the percentage uncertainty in the measurement. By Faraday's Law EMF = rate of change of flux linkage = d Nphicos(theta)/dt = d(Nphi)/dt .cos(theta). We plotted peak emf against cos(theta). We got a reasonable straight line. The gradient will be the peak rate of change of flux linkage.