Actually your question is far from stupid if at all. That's interesting because they didn't teach that one on instrument ground school. I think it is such an important point. Suppose you are in IMC and your airspeed drops to 0 and you turn on pitot heat, nothing. You climb and descend to see if the airspeed will indeed act like an altimeter (like the book said it would), nothing. Either way the AI must be covered ASAP.