Why is it that when driving in a car, and a lightning bolt strikes, my AM radio gets cut off for a while, but FM stays on? I noticed this one day, a lightning/thunder occurred and my Fabulosa Spanish music died for a second. But not FM? 
 A: AM radio typically transmits at around 1 MHz, FM radio at about 90 MHz.  Measurements of the RF spectrum of lightning strikes show a falloff with frequency of about 20 dB per decade in that frequency range, so with FM about 2 decades above AM, you'd expect AM to have about 40dB higher interference from a lightning strike.  In addition to that, FM signals attenuate faster with range, so depending on your distance from the lightning strike the effective AM/FM interference ratio could be even larger.
A: For a more complete answer, one should also consider the basic difference between the two transmission schemes.  AM - i.e Amplitude Modulation - encodes a signal by varying the amplitude of a radio wave of a single frequency.  FM - i.e. Frequency Modulation - encodes a signal by varying the frequency itself within a narrow range about a central value.  When lightning strikes, the electrical discharge generates a lot of radio noise at a set of frequencies; if one of those matches the AM frequency you are tuned to, the amplitudes add, messing up the whole signal.  By contrast, since FM monitors variation in frequency, it is fairly insensitive to noise in any particular frequency in the monitored range.  (that insensitivity is actually what motivated the invention of FM in the first place)
