Current produced by thermocouples. My understanding is that the thermocouple voltage is strictly a function of the temperature. Apparently this is called the Seebeck Voltage. Like any voltage source there is an internal resistance associated with it due to real world effects.
HIV/AIDS. Condoms for HIV prevention. Condoms, when used correctly and consistently, are highly effective in preventing HIV and other sexually transmitted infections (STIs). A large body of scientific evidence shows that male latex condoms have an 80% or greater protective effect against the sexual transmission of HIV and other STIs.
To answer your question, the contraceptive sponge is 91 percent effective at preventing unintended pregnancy if used correctly and consistently. If use is less than perfect and/or used inconsistently, effectiveness is estimated at 88 percent (more on the difference between the two rates in a bit).