Does a car alternator charge the battery if the engine is left running on idle, or do I need to drive the car? thanks?

With the engine on idle, an alternator probably will charge your battery, but better if you drive it

yeah it will charge, some older style alternators won't charge full rate at idle

You need to drive a vehicle a good 100 miles on the expressway to charge a dead battery. That's if the alternator is working.

Letting a motor idle will never charge a battery.

It does charge but at a lower rate than when the engine is at higher RPMs. However, if you're trying to charge a battery from dead doing it with the alternator isn't a good idea. The alternator is designed to compensate for what your engine, lights and electronics use in order to keep the battery at a full charge. It is NOT designed to charge a dead battery and doesn't do a good job of it. You'd need to drive it all day to even get it close to being charged and then it depends on what electronics you're using as that will suck off some of the alternators output. If the battery is dead you really should have it charged with an external battery charger while the engine is off.

Yes just not as much as when you drive it

Yes. Alternators charge effectively on tick over.,

Yes. The alternator works off the engine; not the wheels. A faster running engine can charge the battery faster, but it is not required (and I have no idea how much.)

Both.

it charges at idle. as long as the alternator is turning

Yes, but might be less effective.