A bar magnet is dropped vertically downwards through a long solenoid, which is connected to an oscilloscope (Figure 26.24). The oscilloscope trace shows how the e.m.f. induced in the coil varies with time as the magnet accelerates downwards.

a. Explain why an e.m.f. is induced in the coil as the magnet enters it (section AB of the trace).
b. Explain why no e.m.f. is induced while the magnet is entirely inside the coil (section BC).
c. Explain why section CD shows a negative trace, why the peak e.m.f. is greater over this section, and why CD represents a shorter time interval than AB.

Transcribed Image Text:

a solenoid E.m.f. CD AB Time