How to tell if a car charger is for ipod or ipad?

We have several car chargers, and they all fit into the ipod and the ipad we have. However, it's my understanding that you can charge an ipod with an ipad charger, but shouldn't do the opposite (charge an ipad with an ipod charger) because the ipod chargers are not as powerful as the ipad chargers. One answer in this forum said charging an ipad with an ipod charger will cause the cable and charger to heat up because it's trying to deliver enough power for the ipad but is only designed to deliver power for an ipod (less power than the ipad).

So how do I identify which of our chargers is which, and is it the part that plugs into the car or the part that plugs into the ipod/ipad that is different? Some of our chargers are in two pieces - 1 piece plugs into the car and has USB port, the other piece plugs into the USB port on one end and the device on the other end. We also have chargers that are just one piece - one end plugs into the car, the other end plugs into the device.

I guess I'm asking how do I identify something that should only be used on the ipod (delivers less power than the ipad needs)?

Thanks for educated clarification.

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