One way to determine a magnetic field strength is to measure the emf induced in a rotating coil. To calibrate a large magnet in your laboratory, you attach a 2.0-cm-diameter, 100-turn coil to the end of a motor-driven shaft, place the coil between the pole tips of the magnet, and rotate it at different frequencies. The emf oscillates, so you use a voltmeter that measures its amplitude. The table shows your data:

Frequency (Hz).................Voltage (mV)

10..........................................380

15..........................................610

20..........................................780

25........................................1020

30........................................1160

Use an appropriate graph of the data to determine the magnetic field strength.